2-(p-ALKOXYPHENYL)-2-IMIDAZOLINES AND THEIR USE AS CORROSION INHIBITORS

ABSTRACT

An aminoalkyl imidazolines of the formula: 
     
       
         
         
             
             
         
       
     
     having p-octyloxy-, p-dodecyloxy-, or p-octadecyloxy-phenyl pendants as hydrophobes, for use to mitigate mild steel corrosion. An electron-rich aromatic ring, in conjugation with an amidine motif, imparts increasing corrosion inhibition efficiencies with an increasing hydrophobe chain length. X-ray photoelectron spectroscopy confirms the formation of an aminoalkyl imidazoline film on a metal surface prior to reaching a critical molar concentration.

BACKGROUND OF THE INVENTION

The present disclosure is directed to the synthesis and preparation ofimidazoline compounds and their use as corrosion inhibitors in metallicflow lines.

DESCRIPTION OF THE RELATED ART

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

The oil and gas industries experience huge economic losses as a resultof the damage corrosion inflicts on pipes, and other plants systems. [S.Nesic, Key issues related to modelling of internal corrosion of oil andgas pipelines-A review, Corros. Sci. 49 (2007) 4308-4338. Incorporatedherein by reference in its entirety.] Corrosion can be defined as thegradual degredation of a material by a chemical reaction of saidmaterial with its environment. It is noticeably problematic formaterials that comprise a metal, as it can compromise, or even destroy,many of the metal's useful properties such as strength and appearance.In particular, corrosion has a detrimental effect on a metallic surface,such as the surfaces of steel sheeting and pipes, when these surfacesare placed in contact with petroleum and/or petroleum products.

Petroleum, herein defined as crude oil, has many constituents. Thenatural constituents of crude petroleum are known as petroleum products.These include, but are not limited to, gasoline, jet fuel, diesel fuel,heating oil, and other heavy fractions which result in the production ofasphalt, tar, and paraffin wax. Surprisingly, although known to bevulnerable to corrosion, metals such as steel are commonly usedthroughout the petroleum industry to form the majority of pipelinestransporting petroleum and petroleum products.

Steel itself can be classified by elasticity parameters and carboncontent. For example, mild steel is an alloy comprised of metals andnon-metals, along with a high amount of carbon. The oil and gasindustries rely heavily on this type of steel to form pipes andpipelines in order to transport crude and refined oil. As such, theseindustries are increasingly concerned with the need to minimizecorrosion in light of high economic replacement costs and ever-growingenvironmental safety concerns.

Environments that are warm, halic, and acidic are generally morecorrosive to metals than those that are cooler, non-halic, and alkaline.Metal surfaces, in particular, experience electrochemical oxidation, orcorrosion, when exposed to acidic (low pH) surroundings. This type ofcorrosion is particularly aggravated when metal parts and surfaces arein continuous contact with acidic aqueous environments, such as thoseoccurring within pipelines carrying petroleum and/or petroleum productswhich have been obtained through an enhanced oil recovery process.

Enhanced oil recovery is defined as the implementation of varioustechniques for increasing the amount of crude oil that can be extractedfrom an oil field. Several techniques exist; however, gas injection, ormiscible flooding, is presently the most commonly used approach inenhanced oil recovery. The term miscible flooding refers specifically toan injection processes that introduce miscible gases into a reservoirresulting in a displacement process. This displacement process maintainsthe reservoir pressure and moreover improves oil displacement, thusincreasing oil recovery.

Although various gases can be used for miscible flooding, hydrogensulfide and carbon dioxide are the favored choices due to their low costand viscosity reducing properties. Consequently, the corrosiveenvironment encountered in oil wells is either anaerobic or aerobic, andcontains ‘sour’ (containing hydrogen sulfide) or sweet (containingcarbon dioxide) corrosive components.

“Sweet corrosion” can be further defined as the corrosion of carbon andlow-alloy steel by carbonic acid and its derivatives. It is thereforeevident that the high levels of CO₂ and/or H₂S introduced duringmiscible flooding result in the formation of acidic aqueous conditions.Notably, contact between the metal surfaces of a pipeline system and theaqueous acidic petroleum products of an enhanced oil recovery process,can occur during all phases of hydrocarbon recovery and refining. Alloytechnology has recently provided materials that can withstand theincidental contact of steel with corrosive components such as NaCl, CO₂and/or H₂S, but the corrosion problem is intensified when there is nochoice but to continuously contact steel with these components, as inthe case of hydrocarbon exploration, recovery, and refining.

In addition to the level of acidity or alkalinity within a transportpipeline system, the level of corrosion is influenced by several otherfactors. These include, but are not limited to, the metallurgy and ageof the pipeline, the temperature and pressure at which the pipeline isoperated, the flow patterns, water accumulation, and turbulent intensityof the flow, the fluid chemistry concerning CO₂, H₂S, O₂, and NaClcontent, the inherent corrosiveness of the fluid flowing through thepipeline, and the presence, or lack of, an inhibitor, and the ability ofan existent inhibitor to maintain adhesion to the surface of the pipe inthe transport pipeline system.

Metallurgy refers in part to the chemical composition and surfacemorphology of the pipeline. If mild steel is exposed to an aeratedneutral aqueous solution, such as a dilute solution of sodium chloridein water, a corrosive attack will begin at any defects found in apreviously formed oxide film on said mild steel. These defects may bepresent as a result of mechanical damage such as scratches, or may bedue to natural discontinuities in the film, i.e. inclusions, grainboundaries or dislocation networks at the surface of the steel.

At each defect the steel is exposed to the solution (electrolyte), ananodic reaction will occur, resulting in the formation of iron ions andfree electrons. These electrons are then conducted through the oxidefilm to take part in a cathodic reaction at the surface of the film.This reaction requires the presence of dissolved oxygen in theelectrolyte which furthers a response favoring the formation of hydroxylions. Thus, the surface morphology plays a distinct role in initiatingthe anodic reaction of a corrosive process.

Several methods exist to limit both the occurrence and progression ofcorrosion. They include the selection of a corrosion resistant materialfor the pipeline, such as stainless steel, plastics, and special alloys.Inert barriers, such as coatings and linings that are placed between thepipe wall and the flowing fluid also limit corrosion. These barriers areoften applied in conjunction with cathodic protection systems.Additional measures include the use of chemical corrosion inhibitors.Chemical corrosion inhibitors are injected into the pipeline to reducethe pH, act as a barrier, and react with possible oxidizing agents. Assuch, chemical corrosion inhibitors have been the subject ofconsiderable research.

In general, the choice of a corrosion inhibitor varies according to thenature of the corrosive environment. For example, in order to transportpetroleum products, the oil industry uses large-diameter flow lines inoil field applications. Pipelines in these situations can transportlarge volumes of produced oil and water at extremely high flow ratesfrom the field to a processing station at rates ranging up to 50 m/sec.The ability of an added corrosion inhibitor to completely cover theinterior of the line, and subsequently, the ability of the addedcorrosion inhibitors to maintain adhesion to the interior of the line,depends on both the chemical adhesive properties of the inhibitor andthe shear stress conditions which exist inside the line. Understandably,corrosion inhibitors with good adhesive qualities under high shearstress conditions are therefore necessitated.

Due to the eco-toxicity of many corrosion inhibitors, it is essential touse those inhibitors which are active at a concentration that does notharm the environment. Gas and oil production processes often take placeoffshore or along a coastline. If a corrosion inhibitor enters the seaor a stretch of fresh water, it can potentially harm microorganisms, andother aquatic life, and thus detrimentally effect the environment.Recent attempts have therefore been made to identify successfulcorrosion inhibitors which are less toxic to the environment thanpreviously known inhibitors.

Many relevant inhibitor compositions are based upon amines, amides, orimidazolines; often in combination with other types of inhibitors.Imidazoline corrosion inhibitors exhibit both high efficiency and lowtoxicity, and furthermore, are advantageously synthesized fromenvironmentally friendly raw materials.

In addition to their use in the petroleum industry, imidazolines canalso limit corrosion in a solvent-based post combustion capture system,such as those which release large sources of CO₂ emissions. Theseinclude, but are not limited to, such systems as coal-fired powerplants, refineries, cement manufacturing and the like, where corrosioncan affect every part of the process equipment. Imidazolines can also beemployed as inhibitors of corrosion formed on metallic surfacesresulting from exposure to a steam condensate. Examples include thosegenerated from steam generating systems such as steam boilers, coolingwater systems, and heat transfer water systems.

Currently, imidazolines are the most extensively used inhibitors tocombat CO₂ corrosion. [V. Jovancicevic, S. Ramachandran, P. Prince,Inhibition of carbon dioxide corrosion of mild steel by imidazolines andtheir precursors, Corrosion 55 (1999) 449-455. X. Liu, S. Chen, H. Ma,G. Liu, L. Shen, Protection of iron corrosion by stearic acid andstearic imidazoline self-assembled monolayers, Appl. Surf. Sci. 253(2006) 814-820. X. Liu, P. C. Okafor, Y. G. Zheng, The inhibition of CO₂corrosion of N80 mild steel in single liquid phase and liquid/particletwo-phase flow by aminoethyl imidazoline derivatives, Corros. Sci. 51(2009) 744-751. P. C. Okafor, X. Liu, Y. G. Zheng, Corrosion inhibitionof mild steel by ethylamino imidazoline derivative in CO₂-saturatedsolution, Corros. Sci. 51 (2009) 761-768. F. Farelas, A. Ramirez, Carbondioxide corrosion inhibition of carbon steels through bis-imidazolineand imidazoline compounds studied by EIS, Int. J. Electrochem. Sci. 5(2010) 797-814. M. W. S. Jawich, G. A. Oweimreen, S. A. Ali,Heptadecyl-tailed mono- and bis-imidazolines: A study of the newlysynthesized compounds on the inhibition of mild steel corrosion in acarbon dioxide-saturated saline medium, Corros. Sci. 65 (2012) 104-112.Incorporated herein by reference in their entirety.]

Imidazolines are defined as a class of heterocycles formally derivedfrom imidazoles by the addition of H₂ across one of two double bonds.Three isomers are known: 2-imidazoline, 3-imidazoline, and4-imidazoline. The 2- and 3-imidazolines contain an imine center and the4-imidazoline contains an alkene group.

The chemical architecture of an imidazoline inhibitor frequentlyincludes the following: a five-membered heterocycle containing anelectron-rich hydrophilic amidine (N═C—N) group, a pendent side chaincontaining one or more electron-donor hydrophilic functional group(s)(R₁) and a hydrophobic alkyl chain (R₂) attached to the carbon atom ofthe amidine group, respectively (1).

The ring-nitrogens in imidazolines of structure (2) are weaklynucleophilic but are strong bases in compounds such as1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (pK_(b) 1.1) and1,5-Diazabicyclo[4.3.0]non-5-ene (DBN) (pK_(b) 0.5). [P. A. Koutentis,M. Koyioni, S. S. Michaelidou, Synthesis of[(4-Chloro-5H-1,2,3-dithiazol-5-ylidene)amino]azines, Molecules 16(2011) 8992-9002. Incorporated herein by reference in its entirety.]

In the presence of CO₂, the bases are reported to form bicarbonate salts(3) in aqueous media [W. Qiao, Z. Zheng, Q. Shi, Synthesis andproperties of a series of CO₂ switchable surfactants with imidazolinegroup, J. Surfact. Deterg. 15 (2012) 533-539 D. J. Heldebrant, P. G.Jessop, C. A. Thomas, C. A. Eckert, C. L. Liotta, The Reaction of 1,8Diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide, J. Org. Chem.70 (2005), 5335-5338. Incorporated herein by reference in theirentirety.] Imidazolines, upon partial hydrolysis in aqueous solution,are converted into amides (4) [W. Qiao, Z. Zheng, Q. Shi, Synthesis andproperties of a series of CO₂ switchable surfactants with imidazolinegroup, J. Surfact. Deterg. 15 (2012) 533-539 Incorporated herein byreference in its entirety].

The reaction of an amine having a pK_(b) of ≈4 in aqueous CO₂ solutionis complex; [N. Ramachandran, A. Aboudheir, R. Idem, P.Tontiwachwuthikul, Kinetics of the absorption of CO₂ into mixed aqueousloaded solutions of monoethanolamine and methyldiethanolamine, Ind. Eng.Chem. Res. 45 (2006) 2608-2616. P. N. Sutar, A. Jha, P. D. Vaidya, E. Y.Kenig, Secondary amines for CO₂ capture: A kinetic investigation usingN-ethylmonoethanolamine, Chem. Eng. J. 207-208 (2012) 718-724.Incorporated herein by reference in their entirety.] in addition to theformation of carbamate salts 5a & 5b, and bicarbonate salt 6, severalionic and neutral species such as HCO₃ ⁻, CO₃ ²⁻, OH⁻, H₃O⁺, CO₂ and H₂Oare also known to coexist. Due to the large number of compounds (1-6)and additional ionic species, it is difficult to ascertain withcertainty which of the compounds (1-6) and/or ionic species are involvedin imparting inhibitory properties, and thus, the mechanism by which animidazoline imparts corrosion inhibition is complex and poorlyunderstood.

Crude oil itself is corrosive to mild steel; CO₂/H₂O, injected into oilwells to increase production, [X. Jiang, Y. G. Zheng, D. R. Qu, W. Ke,Effect of calcium ions on pitting corrosion and inhibition performancein CO₂ corrosion of N80 steel, Corros. Sci. 48 (2006) 3091-3108Incorporated herein in its entirety.] has been found to be moreaggressive than hydrochloric acid at the same pH. [G. Zhang, C. Chen, M.Lu, C. Chai, Y. Wu, Evaluation of inhibition efficiency of animidazoline derivative in CO₂-containing aqueous solution, Mater. Chem.Phys. 105 (2007) 331-340. U. Lotz, L. Van Bodegom, C. Ouwehand, Theeffect of type of oil or gas condensate on carbonic acid corrosion,Corrosion 47 (1991) 635-644. Incorporated herein by reference in theirentirety.] It is not the dry CO₂, but rather its aqueous solution, whichimparts corrosiveness. The enhanced corrosion is attributed to theincreased cathodic reduction of the species H⁺, HCO₃ ⁻ as well as H₂CO₃,all of which are involved in mobile equilibria in an aqueous solution ofCO₂. [F. F. Eliyan, A. Alfantazi, On the theory of CO₂ corrosionreactions—Investigating their interrelation with the corrosion productsand API-X100 steel microstructure, Corros. Sci. 85 (2014) 380-393. Q. Y.Liu, L. J. Mao, S. W. Zhou, Effects of chloride content on CO₂ corrosionof carbon steel in simulated oil and gas well environments, Corros. Sci.84 (2014) 165-171. Incorporated herein by reference in their entirety.]

The main reactions on the surface of the metal are represented by Eqs.(1)-(5) [F. F. Eliyan, A. Alfantazi, On the theory of CO₂ corrosionreactions—Investigating their interrelation with the corrosion productsand API-X100 steel microstructure, Corros. Sci. 85 (2014) 380-393. Q. Y.Liu, L. J. Mao, S. W. Zhou, Effects of chloride content on CO₂ corrosionof carbon steel in simulated oil and gas well environments, Corros. Sci.84 (2014) 165-171. K. Chokshi, W. Sun, S. Nesic, Iron carbonate scalegrowth and the effect of inhibition in CO₂ corrosion of mild steel, NACEInternational Corrosion Conference & Expo, Paper #05285, 2005.Incorporated herein by reference in their entirety]:

Fe(s)+2H₂CO₃(aq)⇄Fe(HCO₃)₂(aq)+H₂(g)  (1)

Fe(s)+2H⁺(aq)⇄Fe²⁺(aq)+H₂(g)  (2)

Fe²⁺(aq)+2H₂O⇄Fe(OH)₂(s)+2H⁺(aq)  (3)

Fe(OH)₂(s)⇄FeO(s)+H₂O  (4)

Fe(HCO₃)₂(aq)⇄FeCO₃(s)+H₂CO₃(aq)  (5)

A coating of iron (II) carbonate on the metal surface is beneficial asit can minimize the rate of the corrosion process. [J. Han, D. Young, H.Colijn, A. Tripathi, S. Nesic, Chemistry and structure of the passivefilm on mild Steel in CO₂ corrosion environments, Ind. Eng. Chem. Res.48 (2009) 6296-6302. Incorporated herein by reference in its entirety.]The solubility of iron (II) carbonate increases with an increase intemperature, while it dissolves at a lower pH values. Corrosioninhibitors, especially organic compounds containing electron-richhetero-atoms, and alkyl chain hydrophobes, [F. Farelas, M. Galicia, B.Brown, N. Nesic, H. Castaneda, Evolution of dissolution processes at theinterface of carbon steel corroding in a CO₂ environment studied by EIS,Corros. Sci. 52 (2010) 509-517. Incorporated herein by reference in itsentirety.] are used to minimize mild steel corrosion. The inhibitormolecules may undergo physi- and/or chemisorption and form a hydrophobicbarrier film to shield the hydrophobes from the hostile corrosive media.[F. Bentiss, M. Triasnel, H. Vezin, M. Lagrenee, Linear resistance modelof the inhibition mechanism of steel in HCl by triazole and oxadiazolederivatives: Structure-activity correlations, Corros. Sci. 45 (2003)371-380. Incorporated herein by reference in its entirety.]

The effects of hydrophilic and hydrophobic substituents of imidazolineson their inhibition efficiency (IE) have been discussed in some detail.[V. Jovancicevic, S. Ramachandran, P. Prince, Inhibition of carbondioxide corrosion of mild steel by imidazolines and their precursors,Corrosion 55 (1999) 449-455, A. Edwards, C. Osborne, S. Webster, D.Klenerman, M. Joseph, P. Ostovar, M. Doyle, Mechanistic studies of thecorrosion inhibitor oleic imidazoline, Corros. Sci. 36 (1994) 315-325.S. Ramachandran, B. L. Tsai, M. Blanco, H. Chen, Y. Tang, W. A. Goddard,III, The SAM mechanism for corrosion inhibition of iron by imidazolines,Langmuir 12 (1996) 6419-6428. X. Zhang, F. Wang, Y. He, Y. Du, Study ofthe inhibition mechanism of imidazoline amide on CO₂ corrosion of Armcoiron, Corros. Sci. 43 (2001) 1417-1431. D. Wang, S. Yong, M. Wang, H.Xiao, Z. Chen, Theoretical and experimental studies of structure andinhibition efficiency of imidazoline derivatives, Corros. Sci. 41 (1999)1911-1919. Incorporated herein by reference in their entirety.] Somesuggest a greater role played by the N pendent [A. J. Szyprowski,Hydrogen sulphide corrosion of steel—Mechanism of action of imidazolineinhibitors, Proceeding of the Eighth European Symposium on CorrosionInhibitor (8SEIC) Univ. Ferrara, (1995) 1229-1238. Incorporated hereinby reference in its entirety.], while others indicate the opposite [A.Edwards, C. Osborne, S. Webster, D. Klenerman, M. Joseph, P. Ostovar, M.Doyle, Mechanistic studies of the corrosion inhibitor oleic imidazoline,Corros. Sci. 36 (1994) 315-325. Incorporated herein by reference in itsentirety.] There are also contradictory reports on the importance of thelength of the hydrophobic alkyl chain on corrosion inhibition. [V.Jovancicevic, S. Ramachandran, P. Prince, Inhibition of carbon dioxidecorrosion of mild steel by imidazolines and their precursors, Corrosion55 (1999) 449-455. S. Ramachandran, B. L. Tsai, M. Blanco, H. Chen, Y.Tang, W. A. Goddard, III, The SAM mechanism for corrosion inhibition ofiron by imidazolines, Langmuir 12 (1996) 6419-6428. Incorporated hereinby reference in their entirety.] The inhibition efficacy of theimidazolines is attributed to their ability to form a chemisorbed filmon the iron surface. [V. Jovancicevic, S. Ramachandran, P. Prince,Inhibition of carbon dioxide corrosion of mild steel by imidazolines andtheir precursors, Corrosion 55 (1999) 449-45522. Edwards, C. Osborne, S.Webster, D. Klenerman, M. Joseph, P. Ostovar, M. Doyle, Mechanisticstudies of the corrosion inhibitor oleic imidazoline, Corros. Sci. 36(1994) 315-325. Incorporated herein by reference in their entirety.] Thepoorly understood and highly complex mechanism of CO₂ corrosion has, inthe past, impeded the design of new molecules as inhibitors. [A.Edwards, C. Osborne, S. Webster, D. Klenerman, M. Joseph, P. Ostovar, M.Doyle, Mechanistic studies of the corrosion inhibitor oleic imidazoline,Corros. Sci. 36 (1994) 315-325. G. McIntire, J. Lippert, J. Yudelson,The effect of dissolved CO₂ and O₂ on the corrosion of iron, Corrosion46 (1990) 91-95. Incorporated herein by reference in their entirety.]

Accordingly, corrosion inhibitors suitable for the protection of metalsexposed to environments containing carbon dioxide, and exhibitingsuperior adhesive qualities under high shear stress conditions, areneeded.

The above-described methods and compounds illustrate conventionaltechniques for preventing and inhibiting corrosion, and include thepreparation and use of imidazolines as corrosion inhibitors.Accordingly, one objective of the present disclosure is to provide aseries of imidazoline compounds and a method for their preparation.

BRIEF SUMMARY OF THE INVENTION

The present disclosure relates to a series of aminoalkyl imidazolines,and formulations thereof, for use as corrosion inhibitors.

In a first embodiment, the present invention is directed to anaminoalkyl imidazoline represented by the following structural formula(I)

wherein m is an integer of 1 to 10; R is a C₁-C₆ alkylene;R₁ is selected from the group consisting of aromatic groups of formula(II)

wherein X is a heteroatom independently selected from the groupconsisting of oxygen and sulfur;

R′₁ thru R′₅ are each independently selected from the group consistingof hydrogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl, arylalkyl,aminoalkyl, and aminoaryl;

further wherein R′₅ is preferably a C₅-C₂₀ alkyl, most preferably aC₈-C₁₈ alkyl;

R₂ and R₃ are each independently selected from the group consisting ofhydrogen, hydroxyl, halogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl,arylalkyl, aminoalkyl, and aminoaryl, (CH₂)₂COOH, CH₂CH(CH₃)COOH andimidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I)comprises a 2-imidazoline ring substituted with an ethanamine group at a5-N position of the 2-imidazoline ring, and a p-octyloxy phenyl group ata 1-C position of the 2-imidazoline ring; so as to provide a1-(2-aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I)comprises a 2-imidazoline ring substituted with an ethanamine group at a5-N position of the 2-imidazoline ring, and a p-dodecyloxy phenyl groupat a 1-C position of the 2-imidazoline ring; so as to provide a1-(2-aminoethyl)-2-(4-dodecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I)comprises a 2-imidazoline ring substituted with an ethanamine group at a5-N position of the 2-imidazoline ring, and a p-octadecyloxy phenylgroup at the 1-C position of the 2-imidazoline ring; so as to provide a1-(2-aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I)comprises a 2-imidazoline ring substituted with aN¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine group at a 5-N position ofthe 2-imidazoline ring, and a p-octyloxy phenyl group at a 1-C positionof the 2-imidazoline ring; so as to provide a1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I)comprises a 2-imidazoline ring substituted with aN¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine group at a 5-N position ofthe 2-imidazoline ring, and a p-dodecyloxy phenyl group at a 1-Cposition of the 2-imidazoline ring; so as to provide a1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazo line of formula (I)comprises a 2-imidazoline ring substituted with aN¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine group at a 5-N position ofthe 2-imidazoline ring, and a p-octadecyloxy phenyl group at the 1-Cposition; so as to provide a1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazoline.

In a further embodiment, the aminoalkyl imidazolines of formula (I) areused in a process for preventing or reducing corrosion of a metallicflow line.

In a further embodiment, the aminoalkyl imidazolines of formula (I) areprepared by reacting a nitrile with a polyethylene polyamine in thepresence of an acid catalyst at a temperature ranging from 140° C.-150°C.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I) isprepared by reacting diethylene triamine (DETA) with 4-(octyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield1-(2-aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I) isprepared by reacting diethylene triamine (DETA) with 4-(dodecyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield1-(2-aminoethyl)-2-(4-dodecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I) isprepared by reacting diethylene triamine (DETA) 4-(octadecyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield1-(2-aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (T) isprepared by reacting tetraethylene pentamine (TEPA) with 4-(octyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield 1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I) isprepared by reacting tetraethylene pentamine (TEPA) with 4-(dodecyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield 1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazoline.

In a preferred embodiment, the aminoalkyl imidazoline of formula (I) isprepared by reacting tetraethylene pentamine (TEPA) with4-(octadecyloxy) cyclohexanecarbonitrile in the presence of a cysteineHCl catalyst at a temperature of 145° C. to yield1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazoline.

In a further embodiment, an aminoalkyl imidazoline of formula (I) ispresent in a composition further comprising one or more additivesselected from the group comprising surfactants, intensifiers, solvents,oil-wetting components, dispersants biocides and/or scale inhibitors.

In another embodiment, the present disclosure includes a method forpreventing or reducing corrosion comprising adding to a process streaman effective corrosion inhibiting amount of one or more aminoalkylimidazolines of formula (I)

wherein m is an integer of 1 to 10; R is a C₁-C₆ alkylene;R₁ is selected from the group consisting of aromatic hydrocarbons offormula (II)

wherein X is a heteroatom independently selected from the groupconsisting of oxygen and sulfur;

R′₁ thru R′₅ are each independently selected from the group consistingof hydrogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl, arylalkyl,aminoalkyl, and aminoaryl;

further wherein R′₅ is preferably a C₅-C₂₀ alkyl, most preferably aC₈-C₁₈ alkyl;

R₂ and R₃ are each independently selected from the group consisting ofhydrogen, hydroxyl, halogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl,arylalkyl, aminoalkyl, and aminoaryl, (CH₂)₂COOH, CH₂CH(CH₃)COOH andimidazoline.

In a further embodiment, the aminoalkyl imidazoline is added to theprocess stream at a dosage of 0.1 ppm to 10,000 ppm by weight of theaminoalkyl imidazoline.

In a further embodiment, the aminoalkyl imidazoline is added to theprocess stream at a dosage of 1.0 ppm to 1000 ppm by weight of theaminoalkyl imidazoline.

In a most preferred embodiment, the aminoalkyl imidazoline is added tothe process stream at a dosage of 1.0 ppm to 500 ppm by weight of theaminoalkyl imidazoline.

In a further embodiment, the process stream comprises at least oneconstituent selected from the group consisting of water, petroleumand/or petroleum products, and at least one constituent selected fromthe group consisting of carbon dioxide (CO₂), hydrogen sulfide (H₂S),oxygen (O₂), and NaCl.

In a further embodiment the aminoalkyl imidazoline is added continuouslyto the process stream.

In a further embodiment the aminoalkyl imidazoline is addedintermittently to the process stream.

In a further embodiment the aminoalkyl imidazoline suppresses an anodicreaction of a metal corrosive process.

In a preferred embodiment, the metal is a mild steel.

In another aspect, the disclosure relates to a method of inhibitingcorrosion of a metal surface undergoing continuous and/or intermittentcontact with a process stream wherein said process stream compriseswater and/or hydrocarbons, comprising;

applying at least one aminoalkyl imidazoline compound of the firstembodiment to a surface of a metal, wherein said applying comprises aspraying or a dipping of a metal surface and/or an adding to saidprocess stream contacting said metal surface, of said imidazoline so asto cover and maintain an effective application on at least one surfaceof a metal in contact with said process stream;

wherein said effective concentration comprises an amount of 0.1 ppm to10,000 ppm by weight of the aminoalkyl imidazoline; preferably 1.0 ppmto 1,000 ppm by weight of, most preferably 1.0 ppm to 500 ppm parts byweight of the aminoalkyl imidazoline;

wherein the aminoalkyl imidazoline is added to a metallic flow linecontinuously or intermittently so as to maintain an effective corrosioninhibiting dose;

wherein said aminoalkyl imidazoline mainly suppresses an anodic reactionof a metal corrosive process.

In a further embodiment, the metallic flow line comprises mild steel.

In a further embodiment, a flow rate of the process stream through themetallic flow line ranges from 0-50 m/sec.

In a further embodiment a flow rate of the process stream through themetallic flow line ranges from 10-30 m/sec.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows an ¹H NMR spectra of the imidazolines (IXa) in CDCl₃.

FIG. 2 shows an ¹H NMR spectra of the imidazolines (VIIIa) in CDCl₃.

FIG. 3 shows a ¹³C NMR spectra of the imidazoline (IXc) in the δ 40-55ppm range in CDCl₃.

FIG. 4 shows a ¹³C NMR spectra of the imidazolines (VIIIc) in the δ40-55 ppm range in CDCl₃.

FIG. 5A shows a potentiodynamic polarization curve(s) at 40° C. for mildsteel in CO₂ saturated 0.5 M NaCl containing various concentrations ofVIIIc, FIG. 5B shows a potentiodynamic polarization curve(s) at 40° C.for mild steel in CO₂ saturated 0.5 M NaCl containing variousconcentrations of IXc, FIG. 5C shows a potentiodynamic polarizationcurve(s) at 40° C. for mild steel in CO₂ saturated 0.5 M NaCl containing50 ppm of VIII a,b,c and FIG. 5D shows a potentiodynamic polarizationcurve(s) at 40° C. for mild steel in CO₂ saturated 0.5 M NaCl containing50 ppm of IX a,b,c.

FIG. 6A shows a Langmuir adsorption isotherm of VIII a, b, c, FIG. 6Bshows a Langmuir adsorption isotherm of IX a, b, c at 40° C., FIG. 6Cshows a Langmuir adsorption isotherm of VIIIc and FIG. 6D shows aLangmuir adsorption isotherm of IXc at various temperatures in CO₂saturated 0.5 M NaCl solution.

FIG. 7 shows a variation of ΔG^(o) _(ads) versus T on mild steel in CO₂saturated 0.5 M NaCl containing VIIIc and IXc.

FIG. 8A shows a “Surface Tension versus Concentration” of imidazolineVIII a,b,c and VIIIa-CO₂, FIG. 8B shows a “Surface Tension versusConcentration” of imidazoline IX a,b,c in 0.5 M NaCl solution, FIG. 8Cshows inhibition efficiency versus concentration of imidazolinesVIIIa,b,c in CO₂ saturated 0.5 M NaCl solution at 40° C., and FIG. 8Dshows inhibition efficiency versus concentration of imidazolines IXa,b,c in CO₂ saturated 0.5 M NaCl solution at 40° C.

FIG. 9A shows an XPS spectrum of Fe after immersing in CO₂ saturated 0.5M NaCl at 40° C. for 6 h in the presence of VIIIc (100 ppm), FIG. 9Bshows an XPS deconvoluted profile of C 1s after immersing in CO₂saturated 0.5 M NaCl at 40° C. for 6 h in the presence of VIIIc (100ppm), FIG. 9C shows an XPS deconvoluted profile of N is after immersingin CO₂ saturated 0.5 M NaCl at 40° C. for 6 h in the presence of VIIIc(100 ppm), FIG. 9D shows an XPS spectrum of Fe in the presence of IXc,FIG. 9E shows an XPS deconvoluted profile of C 1 s in the presence ofIXc, and FIG. 9F shows an XPS deconvoluted profile of N 1s in thepresence of IXc.

FIG. 10A shows an XPS deconvoluted profile of 0 is in the presence of100 ppm of IXa, FIG. 10B shows an XPS deconvoluted profile of Fe 2p inthe presence of 100 ppm of IXb, and FIG. 10C shows an XPS deconvolutedprofile of N is in the presence VIIIb (100 ppm) after immersing Fe inCO₂ saturated 0.5 M NaCl at 40° C. for 6 h.

FIG. 11A shows a ¹³C NMR spectra of VIIIa (in CDCl₃, using TMS asinternal standard), FIG. 11B shows a ¹³C NMR spectra of VIIIa-CO₂ (inD₂O using dioxin as an external standard) and FIG. 11C shows a ¹³C NMRspectra of VIIIa-H⁺(HCO₃ ⁻)CO₂ (in D₂O using dioxin as an externalstandard).

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

Aminoalkyl imidazolines of this disclosure effectively prevent and/orinhibit the formation of corrosion on metal materials and equipment,such as metallic flow lines, used in a process for producing and/ortransporting petroleum and petroleum products. Furthermore, theaminoalkyl imidazolines of this disclosure effectively prevent and/orinhibit the formation of corrosion on metal materials and equipment,such as metallic pipelines, in a process comprising producing and/ortransporting a process stream. The aminoalkyl imidazolines of thisdisclosure also mitigate the corrosion of metal materials and equipmentemployed in related processes wherein steam or other corrosive fluidsand/or gases are contained in a process stream.

Methods of reducing corrosion comprise adding to a process stream aneffective corrosion inhibiting amount of one or more of the aminoalkylimidazolines as disclosed herein. Said processes include, but are notlimited to, processes involving cleaning and hydrocarbon recoveryoperations. With respect to oil and gas production, it is well knownthat during the production life of an oil or gas well, the productionzone, including tubular goods, downhole tools and other equipment withinthe well, may be exposed to corrosive conditions. With respect to theprocess stream, a stream comprising a fluid such as, but not limited to,water, petroleum, petroleum products, and hydrocarbons wherein saidfluid may be found in a liquid or vapor phase in said stream, forms anaqueous and/or petroleum phase. Said stream may further comprise carbondioxide (CO₂), hydrogen sulfide (H₂S,) and/or NaCl, and, in combinationwith the aqueous and/or a petroleum phase, form the process stream.

As an amount of the aminoalkyl imidazoline compounds disclosed hereincan be used to inhibit corrosion of metals in acid and/or alkalineenvironments, the amount that is defined for use is dependent on theparticular environment that it is intended for. A suitable amount, orproportion, or dosage, can be determined empirically by taking intoaccount parameters such as, but not limited to, the nature of theprocess stream and the proportion of corrosive species therein, thenature of the metal being protected, the flow rate of the processstream, the temperature and pressure of said process stream, and theamount of time said metal is contacted by the process stream.

Herein, ppm is defined as the amount of inhibitor as found in a processstream by weight of the inhibitor. The aminoalkyl imidazoline inhibitoris preferably added to the process stream at a dosage of 0.1 ppm to10,000 ppm by weight of the aminoalkyl imidazoline, more preferably at adosage of 1.0 to 1000 ppm by weight of the aminoalkyl imidazoline, andmost preferably at a dosage of 10 to 500 ppm by weight of the aminoalkylimidazoline. Furthermore, the corrosion inhibitors as individuallydisclosed herein may be used singularly (neat), or in combination—withor without blending together- to enhance a corrosion inhibitionperformance.

For handling, injection and distribution, any number or combination ofother components may be added to the herein disclosed aminoalkylimidazolines to formulate them into a liquid form, or otherwiseformulate them in order to enhance their performance. The componentscomprise surfactants, intensifiers, solvents, oil-wetting componentsand/or dispersants. Suitable components, which are also compatible withthe process, include, but are not limited to, water, fatty acid esters,ethylated alcohols, sodium sulfonate, isopropanol, aliphaticdistillates, aromatics, heptane, di-isobutyl ketone, methyl isobutylketone, glycols, high boiling oils, xylene, toluene, and naphtha.

The imidazoline inhibitor may also be used in combination with othermaterials commonly employed in corrosion inhibiting compositions suchas, but not limited to, scale inhibitors and biocides.

The aminoalkyl imidazoline, and any additives such as the abovementioned solvents and/or dispersants, can be injected directly into theprocess stream by, but not limited to, (a) injection at differentlocations into the process stream, (b) as separate formulations injectedat the same location, or (c) injection together as part of a singlecombined formulation. It is also within the scope of this disclosure tohave several injection sites located at various distance intervals alonga pipeline containing a process stream so as to present said aminoalkylimidazolines to a process stream environment in which they are mostsuited to inhibit corrosion. In a preferred embodiment, the aminoalkylimidazolines are added continuously. In another preferred embodiment,the aminoalkyl imidazolines are added intermittently.

In a further embodiment, the adding to a process stream of an effectivecorrosion inhibitor(s) comprises introducing, adding or injecting atleast one imidazoline of this disclosure through a member or conduitpositioned within an initial proximal portion of a pipeline or wellcarrying a process stream. The process stream may contain compounds suchas, but not limited to, water, petroleum, petroleum products,hydrocarbons, and acidic species such as CO₂ and/or H₂S, and NaCl. Themethods herein also encompass a plurality of injection sites located atvarious intervals along said pipeline, or well, carrying said processstream, for additional injection of said imidazoline compounds tailoredto treat corrosion at a specific site of the pipeline or well.

Furthermore, inhibition of a corrosive process of a metal, such as mildsteel, can occur by mitigating the corrosion found at a metal surface incontact with a process stream. Said process stream as previouslydefined, includes, but is not limited to, water, petroleum, petroleumproducts, hydrocarbons, and acidic species such as CO₂ and/or H₂S, andNaCl. Said inhibition of the corrosion comprises administering aneffective concentration of an aminoalkyl imidazoline of this disclosure.Administering comprises applying at least one aminoalkyl imidazolinecompound of the disclosure to a surface of a metal, wherein saidapplying comprises a spraying or a dipping of a metal surface and/or anadding to said process stream contacting said metal surface, of saidimidazoline so as to cover and maintain an effective application on atleast one surface of a metal in contact with said process stream.

The aminoalkyl imidazolines of this invention mainly suppresses ananodic reaction of the metal corrosive process, and maintain adhesion tosaid metal surface when the flow rate of a process stream within a flowline ranges between 0-50 m/sec. Preferably, the aminoalkyl imidazolinesof this invention mainly suppresses an anodic reaction of the metalcorrosive process, and maintain adhesion to said metal surface when theflow rate of a process stream within a flow line ranges between 10-30m/sec.

As used herein the term “alkenyl” is a monovalent group derived from astraight or branched chain hydrocarbon containing one or morecarbon-carbon double bonds. Illustrative alkenyl groups include, but arenot limited to, groups such as ethenyl, propenyl, butenyl, and1-methyl-2-buten-1-yl.

As used herein the term “alkoxy” is an alkyl-O— group where alkyl isdefined herein. Illustrative alkoxy groups include, but are not limitedto, groups such as methoxy, ethoxy, propoxy, butoxy, octyloxy,dodecyloxy and octadecyloxy. Related to alkoxy groups are “aryloxy”groups, which have an aryl group singular bonded to oxygen such as thephenoxy group (C₆H₅O—).

As used herein the term “alkyl” is a monovalent group derived from astraight or branched chain saturated hydrocarbon by the removal of asingle hydrogen atom. Illustrative alkyl groups include, but are notlimited to, groups such as ethyl, n- and iso-propyl, n-, sec-, iso- andtert-butyl, lauryl, octyl, dodecyl, and octadecyl.

As used herein the term “alkylaryl” is an alkyl-arylene-group wherealkyl and arylene are defined herein. Illustrative alkylaryl groupsinclude, but are not limited to, groups such as tolyl, ethylphenyl,propylphenyl, 4-(octyloxy)benzonitrile, 4-(dodecyloxy)benzonitrile, and4-(octadecyloxy)benzonitrile.

As used herein the term “alkylene” is a divalent group derived from astraight or branched chain saturated hydrocarbon by the removal of twohydrogen atoms. Illustrative alkylene groups include, but are notlimited to, groups such as methylene, ethylene, propylene, andisobutylene.

As used herein the term “amino” is a group of formula Y¹Y²N— andquaternary salts thereof where Y¹ and Y² are independently hydrogen,alkyl, aryl, heterocycyl or arylalkyl as defined herein. Y¹ and Y²,together with the N atom to which they are attached may also form aheterocyclyl group. Illustrative amino groups include, but are notlimited to, groups such as amino (—NH₂), methylamino, ethylamino,iso-propylamino, tert-butylamino, dimethylamino, diethylamino,methylethylamino, and piperidino.

As used herein the term “aminoalkyl” is an amino-alkylene-group whereinamino and alkylene are defined herein. Illustrative aminoalkyl groupsinclude, but are not limited to, groups such as 3-dimethylaminopropyl,and dimethylaminoethyl.

As used herein the term “aminoaryl” is an amino-arylene-group whereamino and arylene are defined herein.

As used herein the term “aryl” means substituted and un-substitutedaromatic carbocyclic radicals and substituted and un-substitutedaromatic heterocyclic radicals having 5 to 10 ring atoms. Illustrativearyl groups include, but are not limited to groups such as phenyl, andnaphthyl.

The aryl may optionally be substituted with one or more groups selectedfrom, but not limited to, groups such as hydroxyl, halogen, C₁-C₁₈alkyl, C₁-C₃₀ thiol alkyl and C₁-C₃₀ alkoxy; wherein said alkyl andthiol alkyl is preferably selected from the group consisting of a C₅-C₂₀alkyl; most preferably from the group consisting of a C₈-C₁₈ alkyl.

As used herein the term “arylalkyl” is an aryl-alkylene-group whereinaryl and alkylene are defined herein. Representative arylalkyl include,but are not limited to, benzyl, phenylethyl, phenylpropyl, and1-naphthylmethyl.

As used herein, the term “arylene” is a substituent of an organiccompound that is derived from an aromatic hydrocarbon (arene) that hashad a hydrogen atom removed from a ring carbon atom. Representativearylene include, but are not limited to, phenylene.

As used herein, the term “heterocyclyl” means an aromatic ornon-aromatic monocyclic or multicyclic ring system of about 3 to about10 ring atoms, preferably about 5 to about 10 ring atoms, in which oneor more of the atoms in the ring system is/are element(s) other thancarbon, for example nitrogen, oxygen or sulfur. Preferred ring sizes ofrings of the ring system include about 5 to about 6 ring atoms. Theheterocyclyl is optionally substituted by one or more hydroxy, alkoxy,amino or thiol groups. Representative heterocyclyl rings include, butare not limited to, piperidyl, pyrrolidinyl, piperazinyl, andmorpholinyl.

“Preventing” includes preventing, inhibiting, mitigating and reducing.

Imidazolines comprise a class of nitrogen-containing heterocyclesformally derived from imidazoles by the addition of hydrogen (H₂) acrossone of two double bonds. The 2-imidazoline (dihydroimidazole) of thedisclosure contains an imine center, and is one of three isomers withthe formula C₃H₆N₂.

The 2-imidazoline compound as disclosed herein is substituted at the 5-Nposition and the 1-C position of the 2-imidazoline ring with thefollowing chemical groups, respectively:

-   -   a. A nitrogen containing functional group selected from the        group comprising: an amine, defined as a functional group that        contains a basic nitrogen atom with a lone pair of electrons; a        diamine, comprising a type of polyamine with two amino groups;        or a polyamine, comprising two or more primary amino groups.        Herein, the nitrogen containing functional group is defined as:

wherein m is an integer of 1 to 10 and R is a C₁-C₆ alkylene;

-   -   b. A phenyl ether (phenyl-O—R′₅) or phenyl thiol ether        (phenyl-S—R′₅)

-   -   -   wherein said phenyl ether comprises a phenyl group            p-substituted with orientation to said 2-imidazoline group            with an O—R′₅ group; wherein R′₅ is selected from the group            comprising a C₁-C₃₀ alkyl group; more preferably a C₅-C₂₀            alkyl group, more preferably a C₁₀-C₁₅ alkyl group, more            preferably a C₁₂-C₁₆ alkyl group, most preferably a C₈-C₁₈            alkyl group, so as to provide a p-alkoxy phenyl pendant, or:            -   wherein said phenyl thiol ether comprises a phenyl group                p-substituted with orientation to said 2-imidazoline                group with an S—R′₅ group; wherein R′₅ is selected from                the group comprising a C₁-C₃₀ alkyl group; more                preferably a C₅-C₂₀ alkyl group, most preferably a                C₈-C₁₈ alkyl group so as to provide a p-thiol alkyl                phenyl pendant.

As previously defined herein, the structure of the aminoalkylimidazolines of this disclosure comprise a:

2-imidazoline substituted with:

-   -   an amine, diamine, polyamine, or repeating units thereof, at the        5-N position of the imidazoline ring; and    -   a p-alkoxy phenyl, or    -   a p-thiol alkyl phenyl pendant

The preferred structure of the compound as disclosed herein comprises:

-   -   2-imidazoline substituted with:    -   ethanamine or N¹-(2-aminoethyl)-N²ethylethane-1,2-diamine at the        5-N position of the imidazoline ring,

and a phenyl ether or a phenyl thiol ether group at the 1-C position ofthe 2-imidazoline ring;

-   -   wherein said phenyl ether is para-bonded to an alkyl group        selected from the group consisting of a C₈, C₁₂ or C₁₈ alkyl so        as to form a p-octyloxy-, p-dodecyloxy, or p-octadecyloxy-phenyl        pendant, or    -   wherein said phenyl thiol ether is para-bonded to an alkyl group        selected from the group consisting of a C₈, C₁₂ or C₁₈ alkyl so        as to form a p-octyl(phenyl)sulfane, p-dodecyl(phenyl)sulfane,        or p-octadecyl(phenyl)sulfane pendant.

It is also within the scope of the disclosure to provide furthersubstitutions onto the imidazoline, phenyl and/or phenoxy ring(s) so asto provide a structure comprising the formula:

wherein m is an integer of 1 to 10; R is a C₁-C₆ alkylene; preferably abranched or linear ethylene —CH₂CH₂—, propylene —CH₂CH₂CH₂—, butylene—CH₂CH₂CH₂CH₂—, or pentylene —CH₂CH₂CH₂CH₂CH₂— group,

X is a heteroatom independently selected from the group consisting ofoxygen and sulfur;

R′₁ thru R′₅ are each independently selected from the group consistingof hydrogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl, arylalkyl,aminoalkyl, and aminoaryl, preferably R′₁-R′₄ are hydrogen atoms and R′₅is a C₆-C₈ alkyl group, more preferably a C₁₀-C₃₀ alkyl group, morepreferably a C₁₂-C₁₈ alkyl group, most preferably a C₁₄-C₁₆ alkyl group;

R₂ and R₃ are each independently selected from the group consisting ofhydrogen, hydroxyl, halogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl,arylalkyl, aminoalkyl, aminoaryl, (CH₂)₂COOH, CH₂CH(CH₃)COOH andimidazoline, preferably R₂ and R₃ are hydrogen atoms.

Specific compounds encompassed by the general formula include:1-(2-aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline,1-(2-aminoethyl)-2-(4-odecyloxyphenyl)-2-imidazoline,1-(2-aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline,1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazoline,1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazoline,and1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazoline.

The compounds of the present invention may include stereoisomers such asoptical isomers, diastereoisomers and geometrical isomers, or tautomersdepending upon the mode of substituents. Thus, the compounds of thepresent disclosure include all of the stereoisomers, tautomers, and amixture thereof.

Also, polymorphs, hydrates, and solvates of the compounds of the presentdisclosure are included within the scope of the disclosure.

The synthesis process used to prepare the aminoalkyl imidazolines ofthis disclosure initially involve the preparation of alkyloxybenzoicacids having a formula of R—O—R′CO₂H wherein R is C₂-C₃₀ alkyl oralkenyl, and R′ is an optionally substituted aryl group. The Rhydrophobe is selected from the group comprising a C₁-C₃₀ alkyl;preferably a C₅-C₂₀ alkyl, most preferably a C₈-C₁₈ alkyl. Thealkyloxybenzoic acids are further reacted to obtain an alkoxybenzamide,which is subsequently reacted to obtain an alkoxybenzonitrile. The useof the alkoxybenzonitrile as a starting material for the synthesis of aseries of aminoalkyl imidazolines is described herein. Furthermore, thecorrosion inhibition properties of said compounds are also presentedherein.

The syntheses of the class of imidazolines from p-alkoxybenzonitrile andoligoamines H₂N(CH₂CH₂NH)_(n)—H (n=2 and 4) are outlined in Scheme 2,wherein R is selected from the group consisting of C₈H₁₇, C₁₂H₂₅, andC₁₈H₃₇. Starting nitriles, 4-(octyloxy)benzonitrile (a),4-(dodecyloxy)benzonitrile (b), and 4-(octadecyloxy)benzonitrile (c) areshown below.

Scheme 2: The synthesis of imidazolines from p-alkoxybenzonitrile andoligoamines H₂N(CH₂CH₂NH)_(n)—H (n=2 and 4) wherein R is (a) C₈H₁₇, (b)C₁₂H₂₅, or (c) C₁₈H₃₇.

Polyalkylene polyamines used to prepare the aminoalkyl imidazolines ofthis disclosure have the formula

where R is C₁-C₆ alkylene and m is an integer of 1 to 10. “Polyethylenepolyamine” means a polyalkylene polyamine where R is —CH₂CH₂—.Representative polyalkylene polyamines include diethylene triamine(DETA), triethylene tetramine, tripropylene tetramine, tetraethylenepentamine (TEPA), and pentaethylene hexamine.

Herein an aminoalkyl imidazoline is prepared by reacting analkoxybenzonitrile with diethylene triamine (DETA) in an exact 1:2.5mmolar ratio to yield an1-(2-aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline (VIIIa), an1-(2-aminoethyl)-2-(4-dodecyloxyphenyl)-2-imidazoline (VIIIb), or an1-(2-aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline (VIIIc).

Further herein, an aminoalkyl imidazoline is prepared by reacting analkoxybenzonitrile with tetraethylene pentamine (TEPA) in an exact 1:2.5mmolar ratio to yield an1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazoline(IXa), an1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazoline(IXb), or an 1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazoline (IXc).

An electron-rich p-alkoxyphenyl substituent at the carbon atom of theN═C—N group augments the electron-donor capacity of the N═C—N group; assuch, the effect of increasing electron density of the ring-nitrogens ontheir inhibition efficacies was examined. The alkoxy groups of C₈, C₁₂and C₁₈ alkyl chains were chosen to demonstrate the importance ofhydrophobe chain length on the inhibition of CO₂ corrosion. TheN-pendent groups of CH₂CH₂NH₂ and (CH₂CH₂NH)₂CH₂CH₂NH₂ allow comparisonof these chains and their role in the suppression of the corrosion ofmild steel in CO₂/0.5 M NaCl solutions. The corrosion inhibition studiesof this disclosure utilized potentiodynamic polarizations, gravimetricweight loss and X-ray photoelectron spectroscopy (XPS) to assist inclarifying the inhibition mechanism.

One common structural component in the imidazolines of this disclosureis the placement of an aromatic ring in conjunction with the N═C—Ngroup. This allows the shifting of the charge density from theelectron-rich benzene ring to the imidazolines as shown using structureVIII (Scheme 2). This stabilizing electron movement results in the tworings becoming coplanar. As a result, the electron-rich N═C—N groups,along with the aromatic π-clouds, are thought to undergo strongadsorption by the formation of coordinate-type bonds with the emptyd-orbitals of Fe on the anodic sites of the metal surface. The highlysurface-active imidazolines VIII and IX disclosed herein demonstratedsuperior corrosion inhibition in a CO₂-saturated 0.5 M NaCl, asillustrated in the following tables.

TABLE 1 Results of Tafel plots of a mild steel sample in varioussolutions containing inhibitors VIIIa-VIIIc in 0.5M NaCl saturated withCO₂ at 40° C. Tafel plots Temp Conc. E_(corr) vs. SCE β_(a) β_(c)i_(corr) Sample ° C. (ppm) (mV) (mV/dec) (mV/dec) (μA/cm²) η (%)^(a)Blank^(b) 40 0 −700 41.2 −258 103.6 — VIIIa 40 1 −694 75.2 −141 49.951.8 5 −683 40.0 −166 38.5 62.8 10 −677 44.3 −172 30.9 70.1 20 −671 63.9−181 24.6 76.2 50 −667 45.6 −139 17.3 83.3 100 −665 36.4 −123 8.32 92.0VIIIb 40 1 −691 25.0 −113 51.1 50.7 5 −674 30.9 −128 36.9 64.4 10 −66423.1 −120 26.9 74.0 20 −655 28.9 −136 19.7 80.9 50 −646 25.4 −115 9.6890.6 100 −619 33.1 −127 7.55 92.7 VIIIc 30 0 −692 46.2 −137 93.4 — 1−686 26.1 −119 43.1 53.8 2 −677 33.2 −148 39.1 58.1 3 −663 28.8 −14236.0 61.4 5 −656 25.7 −156 26.7 71.4 10 −651 41.3 −149 21.6 76.8 20 −63030.8 −126 8.9 90.4 40 1 −683 25.5 −114 43.1 58.4 5 −672 34.3 −117 28.372.7 10 −659 47.1 −187 20.8 79.9 20 −651 51.4 −157 8.69 91.6 50 −63639.2 −148 4.81 95.4 100 −620 43.8 −167 1.97 98.1 50 0 −743 39.2 −157124.1 — 1 −728 47.1 −128 65.2 47.5 2 −716 38.5 −146 61.1 50.7 3 −70024.8 −162 56.7 54.2 5 −689 32.3 −125 39.2 68.3 10 −681 29.4 −149 31.674.5 20 −663 37.7 −153 16.3 86.8 ^(a)Inhibition Efficiency, IE (i.e., η)= surface coverage θ. ^(b)The blank was a 0.5M NaCl solution saturatedwith CO₂. ^(c)Inhibitor sample was dissolve in 0.5 cm³ 2-propanol, andadded with 249.5 cm³ blank solution.

TABLE 2 Results of Tafel plots of a mild steel sample in varioussolutions containing inhibitors IXa-IXc in 0.5M NaCl saturated with CO₂at 40° C. Tafel plots Temp Conc. E_(corr) vs. SCE β_(a) β_(c) i_(corr)Sample ° C. (ppm) (mV) (mV/dec) (mV/dec) (μA/cm²) η (%)^(a) Blank^(b) 400 −700 41.2 −258 103.6 — IXa 40 1 −671 61.1 −249 49.2 52.5 5 −660 32.4−146 41.2 60.3 10 −648 57.5 −228 29.1 71.9 20 −645 35.8 −183 22.5 78.250 −641 69.2 −124 19.6 81.1 100 −637 66.7 −238 9.2 91.1 IXb 40 1 −66238.1 −204 47.2 54.4 5 −643 47.2 −260 32.7 68.4 10 −633 35.2 −168 26.474.5 20 −625 56.2 −154 19.5 81.2 50 −609 45.9 −197 14.1 86.5 100 −60541.8 −191 6.35 93.8 IXc 30 0 −692 46.2 −137 93.4 — 1 −683 29.8 −125 42.854.1 2 −674 42.7 −156 35.2 62.4 3 −659 38.5 −129 28.7 69.3 5 −654 42.1−148 20.0 78.5 10 −633 33.0 −134 14.2 84.8 20 −615 36.5 −149 4.13 95.640 1 −668 54.5 −235 45.3 56.3 5 −657 73.1 −194 26.1 74.8 10 −645 87.2−293 20.8 79.9 20 −619 34.6 −148 6.91 93.3 50 −598 37.6 −176 2.82 97.2100 −590 40.6 −212 1.97 98.1 50 0 −743 39.2 −157 124.1 — 1 −711 52.1−153 62.6 49.5 2 −694 39.4 −139 57.8 53.4 3 −671 42.6 −116 44.9 63.8 5−660 29.3 −152 36.2 70.8 10 −638 38.0 −134 28.6 76.9 20 −626 31.9 −14811.4 90.7 ^(a)Inhibition Efficiency, IE (i.e., η) = surface coverage θ.^(b)The blank was a 0.5M NaCl solution saturated with CO₂. ^(c)Inhibitorsample was dissolve in 0.5 cm³ 2-propanol, and added with 249.5 cm³blank solution.

The LPR study revealed θ% values of 73.6, 76.9, and 88.9 at aconcentration of 20 ppm of the DETA-derived imidazolines VIIIa, VIIIb,and VIIIc respectively (Table 3).

TABLE 3 Results of LPR method in 0.5M NaCl saturated with CO₂ at 40° C.Polarization resistance Temp Concentration R′_(p) Sample ° C. (ppm byweight) (Ω cm²) θ^(a) θ (%) Blank^(b) 40 0 89.7 — — VIIIa 40 1 218 0.58958.9 5 247 0.637 63.7 10 276 0.675 67.5 20 340 0.736 73.6 50 568 0.84284.2 100 973 0.908 90.8 VIIIb 40 1 194 0.538 53.8 5 290 0.691 69.1 10315 0.715 71.5 20 388 0.769 76.9 50 653 0.863 86.3 100 1059 0.915 91.5VIIIc 30 0 82.3 — — 1 165 0.502 50.2 2 192 0.572 57.2 3 226 0.635 63.5 5301 0.726 72.6 10 471 0.825 82.5 20 1107 0.925 92.5 40 1 210 0.573 57.35 305 0.706 70.6 10 477 0.812 81.2 20 809 0.889 88.9 50 1317 0.932 93.2100 1800 0.950 95.0 50 0 97.8 — — 1 172 0.431 43.1 2 196 0.500 50.0 3218 0.552 55.2 5 297 0.671 67.1 10 451 0.783 78.3 20 689 0.858 85.8^(a)Surface coverage, θ = Inhibition Efficiency, IE (i.e., η). ^(b)0.5MNaCl solution saturated with CO₂.

For the corresponding TEPA-derived imidazolines IXa, IXb and IXc, therespective θ% at 20 ppm were found to be 74.7, 82.4, and 91.2 (Table 4).

TABLE 4 Results of LPR method in 0.5M NaCl saturated with CO₂ at 40° C.Polarization resistance Temp Concentration R′_(p) Sample ° C. (ppm byweight) (Ω cm²) θ^(a) θ (%) Blank^(b) 40 0 89.7 — — IXa 40 1 162 0.44644.6 5 214 0.581 58.1 10 281 0.681 68.1 20 355 0.747 74.7 50 515 0.82682.6 100 918 0.902 90.2 IXb 40 1 212 0.577 57.7 5 260 0.655 65.5 10 3320.730 73.0 20 509 0.824 82.4 50 540 0.834 83.4 100 1181 0.924 92.4 IXc30 0 82.3 — — 1 169 0.514 51.4 2 213 0.613 61.3 3 256 0.678 67.8 5 3360.755 75.5 10 592 0.861 86.1 20 2562 0.968 96.8 40 1 176 0.493 49.3 5386 0.768 76.8 10 616 0.854 85.4 20 1019 0.912 91.2 50 1695 0.947 94.7100 2045 0.956 95.6 50 0 97.8 — — 1 197 0.504 50.4 2 225 0.565 56.5 3274 0.643 64.3 5 313 0.687 68.7 10 546 0.821 82.1 20 902 0.892 89.2^(a)Surface coverage, θ = Inhibition Efficiency, IE (i.e., η). ^(b)0.5MNaCl solution saturated with CO₂.

At various concentrations of the inhibitors, the pentamine derivativesIX imparted slightly better inhibition efficiencies than their triaminecounterparts VIII. Note that a concentration of 20 ppm of VIIIa, VIIIb,VIIIc and IXa, IXb, IXc translates into their respective concentrationsof 63.0, 53.5, 43.7, 49.6, 43.5, and 36.8 μM, respectively.

A higher polyamine chain length seems to augment the corrosioninhibition to a limited extent. Both VIIIc and IXc having a hydrophobicalkyl chain of C₁₈ show better inhibition efficacies than theirrespective C₈ or C₁₂ counterparts VIIIa, IXa, and VIIIb, IXb. Anincrease in the θ% values with an increasing alkyl chain length may beattributed to the extra coverage of the metal surface made possible bythe longer hydrophobic tails. The results of the Tafel extrapolations(Tables 1 and 2) corroborated the findings of the LPR method (Tables 3and 4). As evident from Table 5, at a concentration of 100 ppm, all theimidazolines imparte very good IEs, especially VIIIc and IXc, where bothhave a η% of over 98.

TABLE 5 Corrosion inhibition efficiency, η (%) using polarizationresistance and Tafel plots of mild steel samples in various solutionscontaining 50 and 100 ppm by weight of the inhibitors in 0.5M NaClsolution saturated with CO₂ (1 atm) at 40° C. η (%) Polarization methodTafel method Compound 20^(a) 50^(a) 100^(a) 20^(a) 50^(a) 100^(a) VIIIa73.6 84.2 90.8 76.2 83.3 92.0 VIIIb 76.9 86.3 91.5 80.9 90.6 92.7 VIIIc88.9 93.2 95.0 91.6 95.4 98.1 IXa 74.7 82.6 90.2 78.2 81.1 91.1 IXb 82.483.4 92.4 81.2 86.5 93.8 IXc 91.2 94.7 95.6 93.3 97.2 98.1 ^(a)inhibitorconcentration in ppm by weight

Referring now to FIGS. 5A, 5B, 5C, and 5D which shows the Tafel plotsfor the imidazolines and their Tafel constants, while corrosionpotentials and IEs are included in Tables 1 and 2. The E_(corr) valuesin all the cases progressively shifted to less negative values (i.e.noble direction) with the increase in the inhibitor concentrations,thereby indicating that the imidazolines are suppressing mainly theanodic reactions as illustrated in FIGS. 5A, 5B, 5C, and 5D. Adifference of E_(corr) values between the blank and inhibited solution(100 ppm) in the ranges 35-72 mV (Table 1) and 57-78 mV (Table 2) for(VIIIa, VIIIb, VIIIc) and (IXa, IXb, IXc), respectively, does notqualify these inhibitors to be classified under anodic type inhibitors.Classification of a compound as a cathodic- or anodic-type inhibitor isfeasible when the E_(corr) is shifted by at least 85 mV [S. Z. Duan, Y.L. Tao, Interface Chemistry. Higher Education Press, Beijing, 1990, pp.124-126. Incorporated herein by reference in its entirety]. Inhibitoraction is more pronounced in the anodic Tafel lines as the differencebetween the anodic current densities in the absence and presence ofinhibitor are much greater than the corresponding differences in thecathodic branches as shown in FIGS. 5A, 5B, 5C, and 5D. The inhibitorsthus retard the anodic dissolution of iron more than the cathodichydrogen evolution reaction. As evident from Tables 1 and 2, thecathodic (β_(c)) and anodic (β_(a)) slopes in most instances are notgreatly affected, thereby implying that the mechanism of the reactionsoccurring at the electrodes are not altered in the presence of theinhibitors. The inhibitors simply block the anodic and cathodic reactionsites. The E_(corr) shifts suggest that the studied compounds in CO₂saturated 0.5 M solution act as mixed-type inhibitors under thepredominance of anodic control. FIGS. 5A, 5B, 5C, and 5D shows that theshift in the anodic direction increases in the order: VIIIa<VIIIb<VIIIcand IXa<IXb<IXc, and the shift in the presence of a pentaamine-derivedinhibitor (IX) were found to be slightly higher than those of atriamine-derived imidazolines (VIII). The negative values of ΔH^(o)_(ads) suggest an exothermic physisorption of the inhibitors on themetal surface, while negative ΔG^(o) _(ads) certify their favorabilty asillustrated in Table 6. [S. Nesic, G. T. Solvi, J. Enerhaug, Comparisonof the rotating cylinder and pipe flow tests for flow-sensitive carbondioxide corrosion, Corrosion 10 (1995) 51773-787. Incorporated herein inits entirety.] The relatively smaller values of −ΔG^(o) _(ads) values inthe range 37-43 kJ/mol, which are greater than 20 kJ/mol, indicate theelectrostatic (i.e. physisorption) and chemisorption adsorptionmechanism of the imidazolines on mild steel [W. Durnie, R. De Marco, A.Jefferson, B. Kinsella, Development of a structure-activity relationshipfor oil field corrosion inhibitors, J. Electrochem. Soc. 146 (1999)1751-1756. S. Z. Duan, Y. L. Tao, Interface Chemistry. Higher EducationPress, Beijing, 1990, pp. 124-126. Incorporated herein by reference inits entirety].

A protective film can be constructed by the formation of at least one‘coordinate type’ chemical bond between d-orbitals of iron and thenon-bonding, as well as the n-electrons, in the electron-richimidazoline group and the aromatic ring. [F. Bentiss, M. Triasnel, M.Lagrenee, The substituted 1,3,4-oxadiazoles: a new class of corrosioninhibitors of mild steel in acidic media. Corros. Sci., 42 (2000)127-146 S. Kertit, B. Hammouti, Corrosion inhibition of iron in 1 M HClby 1-phenyl-5-mercapto-1,2,3,4-tetrazole. Appl. Surf. Sci., 93 (1996)59-66. Incorporated herein by reference in their entirety].

Moderately positive values for the entropy change, ΔS^(o) _(ads),ascertain the favorable increase in randomness as a result of thedisplacement of water molecules from the metal surface as shown in Table6. As the temperature increases, the E_(corr) becomes more negative(less noble), which makes the metal surface more susceptible to mediaattack.

TABLE 6 The values of the adsorption equilibrium constant from Langmuiradsorption isotherms and free energy, enthalpy, entropy changes of themild steel dissolution in the presence of inhibitors VIII and IX in CO₂saturated 0.5M NaCl at various temperatures. Temp K_(ads) × 10⁻⁵ΔG°_(ads) ΔH°_(ads) ΔS°_(ads) Compound (° C.) (L mol⁻¹)^(a) (kJ mol⁻¹)(kJ mol⁻¹) (J mol⁻¹ K⁻¹) VIIIa 40 27083 −37.0 — — VIIIb 40 34995 −37.7 —— VIIIc 30 191106 −40.8 −15.8 +82.5 40 163330 −41.7 50 129573 −42.4 IXa40 32676 −37.5 — — IXb 40 81241 −39.9 — — IXc 30 310441 −42.0 — — 40266094 −43.0 −16.3 +85.0 50 210417 −43.7 ^(a)K_(ads) obtained in L/mgwas converted to L/mol

Some of the anodic polarization curves in the current-vs-potentialplots, especially in the higher concentration range of the inhibitors,have a current-increasing plateau which is called the desorptionpotentials. [F. Bentiss, M. Triasnel, M. Lagrenee, The substituted1,3,4-oxadiazoles: a new class of corrosion inhibitors of mild steel inacidic media. Corros. Sci., 42 (2000) 127-146 W. Jia, A study on theimpedance responses of inhibitor desorption, Chin. J. Oceanol. Limnol.16 (1998) 54-59. Incorporated herein by reference in their entirety.]This is displayed in FIGS. 5A, 5B, 5C, and 5D. Significant steeldissolution occurs at potentials higher than the respective desorptionpotential, thereby suggesting a mechanism by which the inhibitors blockthe anodic sites on the metal surface. The surface coverage data (0)indicate that the adsorption of the imidazolines are fitted best by theLangmuir adsorption isotherm; while some of them followed Temkin as wellas Freundlich adsorption isotherms (Table 7).

TABLE 7 Square of coefficient of correlation (R²) and values of theconstants in the adsorption isotherms of Temkin, Frumkin, Langmuir andFreundlich in the presence of inhibitors VIII and IX in CO₂ Saturated0.5M NaCl solution (LPR data used for the isotherm). Com- Temp TemkinLangmuir Frumkin Freundlich pound (° C.) (R², f) (R²) (R², a) (R²) VIIIa40 0.9260, 14 0.9984 0.7313, −3.5 0.9503 VIIIb 40 0.9912, 12 0.99560.9387, −3.2 0.9843 VIIIc 30 0.9901, 6.9 0.9992 0.8389, −1.1 0.9952 400.9831, 9.4 0.9971 0.8128, −1.9 0.9929 50 0.9848, 6.6 0.9940 0.8105,−0.85 0.9822 IXa 40 0.9954, 10 0.9919 0.9542, −2.4 0.9864 IXb 40 0.9338,13 0.9936 0.7907, −3.4 0.9573 IXc 30 0.9997, 6.6 0.9972 0.8551, −0.780.9948 40 0.9808, 7.0 0.9968 0.9961, −0.73 0.9591 50 0.9874, 7.4 0.99670.7608, −0.99 0.9881

The relatively higher values of the energetic inhomogeneity factor fobtained from the Temkin model signifies a strong dependence of the freeenergy of adsorption (ΔG^(o) _(ads)) on the surface coverage. [B. I.Podlovchenko, B. B. Damaskin, Possible demarcation of adsorptionisotherms based on repulsive interaction and surface inhomogeneity,Elektrokhimiya 8 (1972) 297. A. E. Stoyanova, E. I. Sokolova, S. N.Raicheva, The inhibition of mild steel corrosion in 1 M HCl in thepresence of linear and cyclic thiocarbamides—Effect of concentration andtemperature of the corrosion medium on their protective action, Corros.Sci. 39 (1997) 1595-1604. Incorporated herein by reference in theirentirety.]

The imidazolines performed very well at higher temperature (120° C.) andpressure (10 bar, CO₂) to arrest corrosion in 0.5M NaCl (Table 8).

TABLE 8 Corrosion rates and inhibition efficiencies of various corrosioninhibitors (200 ppm by weight) at 120° C. and 10 bar pressure of CO₂ in0.5M NaCl solution. CR^(b) Average % Solution Coupon^(a) (mm y⁻¹) %Inhibition Inhibition Blank A 2.19 — — B 2.23 — VIIIa A 0.607 72.3 71.8B 0.638 71.4 VIIIb A 0.195 91.1 90.8 B 0.212 90.5 VIIIc A 0.149 93.293.1 B 0.156 93.0 IXa A 0.569 74.0 72.5 B 0.647 71.0 IXb A 0.153 93.092.4 B 0.181 91.9 IXc A 0.153 93.0 93.3 B 0.143 93.6 Q I 80 A 0.429 80.481.0 B 0.410 81.6 ARMOHIB29 A 0.396 81.9 82.7 B 0.368 83.5 ^(a)Two mildsteel coupons A and B having different carbon content and compositions^(b)Corrosion rate

The inhibition efficacy η % of the imidazolines, as determined using twotypes of metal coupons A and B having different elemental compositionsand carbon content, were found to increase in the following order:VIIIc>VIIIb>VIIIa> and IXc>IXb>IXa. The current imidazolines having C₁₂(VIIIb, IXb) and C₁₈ (VIIIc, IXc) alkyl chains, outperformed the twocommercial imidazolines QI80 and ARMOHIB219 (Table 8). The objective ofconstructing a surface tension versus inhibitor concentration profile isto find the imidazoline's CMC which can be used to compare theabsorption pattern on either side of the CMC. The imidazolines, whenfound in an aqueous media, are classified as cationic surfactantsbecause of the involvement of the cationic form B found in equilibriumwith its neutral counterpart A (Scheme 1). [D. Bajpai, V. K. Tyagi,Fatty imidazolines: chemistry, synthesis, properties and theirindustrial application, J. Oleo. Sci. 55 (7) (2006) 319-329.Incorporated herein by reference in its entirety].

In terms of molar concentration, the CMC, as well as surface tension ofthe imidazolines, are found to follow the order of: VIIIa>VIIIb>VIIIc;IXa>IXb>IXc; and VIII>IX (Table 9). In an aqueous 0.5 M NaCl solution,the pentamine derivatives IX a-c, having greater hydrophilic polarheads, are expected to have greater CMC values for being more soluble inwater as compared to their triamine counterparts. The increase in thehydrophobic alkyl chain length decreases the solubility of theimidazolines, and, as expected, decreases the CMC. [W. Wang, M. L. Free,D. Horsup, Prediction and measurement of corrosion inhibition of mildsteel by imidazolines in brine solutions. Metall. Mater. Trans. B, 36(2005) 335-341. Incorporated herein by reference in its entirety.] TheC₁₈ alkyl tails, by virtue of having the greater hydrophobicinteractions, lead to smaller CMC values for the imidazolines VIIIc andIXc. Imidazoline VIIIa in CO₂— saturated 0.5 NaCl has a CMC value of37.4 μM (≈11.9 ppm), whereas in the absence of CO₂, it becomes 30.2 μM(≈9.59 ppm). The formation of a carbamate salt of an imidazoline in aCO₂-saturated NaCl solution makes it more water-soluble, hence increasesthe CMC value (vide infra). A closer look at the CMC values FIGS. 8A and8B and Table 9, and the surface coverage (0) data FIGS. 8C and 8D, andTables 3 and 4, reveals that imidazolines cover a majority of thesurface before the concentrations reach their CMC values.

TABLE 9 Surface properties of imidazolines VIII and IX in 0.5M NaCl at40° C. Surface tension C_(cmc) C_(cmc) ΔG°_(mic) Compound (mN m⁻¹) (μmolL⁻¹) (ppm) (kJ mol⁻¹) VIIIa 33.5 30.2 9.59 −27.1 VIIIa^(a) 35.0 37.411.9 −26.5 VIIIb 31.5 21.8 8.14 −27.9 VIIIc 29.3 20.0 9.15 −28.2 IXa36.2 22.4 8.99 −27.9 IXb 34.0 18.3 8.38 −28.4 IXc 31.2 13.9 7.53 −29.1^(a)0.5M NaCl saturated with C0₂

An adsorption on the metal surface is favored over a micellization sincethe ΔG^(o) _(ads) values are more negative (Table 6) when compared withthe corresponding ΔG^(o) _(mic) (Table 9). The monolayer formation atthe interface between the metal and solution is complete before the CMC;after which multilayer coverage, as a result of adsorption of themicelles, may impart further protection albeit to a lesser degree. [4 K.Esumi, M. Ueno, Structure Performance Relationships in Surfactants.Marcel Dekker Press, 2003. Incorporated herein by reference in itsentirety.]

The XPS survey scan composition of Fe immersed in an inhibited solutionof 0.5 M NaCl—CO₂ revealed the presence of a carbonaceous film at themetal surface as indicated by its high carbon and small Fe contents(Table 10).

TABLE 10 XPS survey scan composition of Fe immersed in inhibitedsolution of 0.5M NaCl—CO₂ (1 atm) at 40° C. for 4 h. Approx. Compositionbinding energy (atom %) Peak (eV) 8a 8b 8c 9a 9b 9c C 1s 285.4 24.6 30.834.9 28.7 45.0 32.3 C 1s 286.4 37.8 32.7 24.8 22.8 19.1 24.3 O 1s 530.19.0 9.0 4.0 11.5 4.5 11.5 O 1s 531.5 26.5 14.4 1.6 5.7 O 1s 532.9 19.419.2 1.2 23 16.9 O1s 534.4 9.5 11.4 N 1s 400.0 4.7 5.2 5.0 N 1s 400.63.3 1.1 4.4 5.5 Fe 2p 706.3 0.2 0.4 Fe 2p 711.0 1.4 1.9 2.3 4.2 1.5 3.3Fe 2p 714.3 0.78 0.4 0.6 0.8 0.5 0.5 Cl 2p 197.55 0.92 1.7 199.19

The presence of N (Nitrogen) points (FIGS. 9C, 9F, 10C) its origin tothe imidazolines; the metal surface is thus covered by a film ofimidazolines. The XPS spectra, for example, in the presence ofinhibitors VIIIc and IXc, are shown in FIG. 9A and FIG. 9D,respectively.

The XPS deconvoluted profiles of a C 1s spectrum for VIIIc and IXcrevealed a two-peak profile (FIGS. 9B and 9E); the peak at 285.4 eV wasassigned to the C—C aliphatic bonds, while the presence of C═C, C═O, andC—N bonds were reflected by the peak at 286.4 eV. The presence of 0 ispeaks at 530.1 and 531.5 eV is attributed to the O²⁻ in Fe₂O₃ andhydrous iron oxide FeOOH, respectively (FIG. 10A). [O. Olivares-Xometl,N. V. Likhanova, M. A. Dominguez-Aguilar, J. M. Hallen, L. S. Zamudio,E. Arce, Surface analysis of inhibitor films formed by imidazolines andamides on mild steel in an acidic environment, Appl. Surf. Sci. 252(2006) 2139-2152. M. Tourabi, K. Nohair, M. Traisnel, C. Jama, F.Bentiss, Electrochemical and XPS studies of the corrosion inhibition ofcarbon steel in hydrochloric acid pickling solutions by3,5-bis(2-thienylmethyl)-4-amino-1,2,4-triazole, Corros. Sci. 75 (2013)123-133. Incorporated herein by reference in their entirety.] The otherO 1s peaks at 532.9 and 534.3 may be associated with the oxygen ofadsorbed water. Small intensity peaks at 711 and 706.3 are indicative ofthe presence of Fe³⁺(2p) and Fe^(o) (2p) (FIG. 10B). The peak locatedaround 714.3 is indicative of the presence of a small concentration ofFeCl₃.

Imidazolines VIIIb and IXb, as shown in Scheme 3, both have hydrophobelengths equivalent to 17 CC bonds. At concentrations of 1, 5 and 10 ppm,they are found to impart better corrosion protection than theircorresponding imidazolines having heptadecyl (C₁₇) alkyl chains X andXI, respectively.

Results of the comparative inhibition behaviors of imidazolines havingsimilar pendent chain length 8b versus 10 and 9b versus 11 are shown inTable 11 below.

TABLE 11 η % at concentration (ppm) of Imidazoline 1 5 10 20 50 VIIIb53.8 69.1 71.5 76.9 86.3 X 23.1 54.0 64.7 — 84.5 IXb 57.7 65.5 73.0 82.483.4 XI <14.3 <49.9 65.4 87.2 90.2

The length of the benzene ring is considered an equivalent to four CCbonds and O is assumed to be an equivalent of C. Aminoalkyl imidazolinesVIIIc and IXc, having hydrophobes equivalent to 23 CC bonds, achievedsuperior results when compared with imidazolines VIIIa,b and IXa,b ofthis disclosure (Tables 3-5).

A study to determine the chemical behavior of the imidazolines inaqueous CO₂ was performed. An initial ¹³C NMR spectra of VIIIa in CDCl₃using TMS as an internal standard is shown in FIG. 11A. Subsequently,the chemical behavior of the imidazolines in aqueous CO₂ wasinvestigated using the following procedure: CO₂ was passed through amixture of VIIIa (65 mg) in D₂O (0.8 cm³) at 40° C. for 5 min. The ¹³CNMR spectrum revealed the presence of four signals at the chemicalshifts of 161.0, 163.0, 164.4 and 167.3 ppm, assigned to the carbonsmarked as HCO₃ ⁻, i, k, and e, respectively in FIG. 11B. The assignmentof HCO₃ ⁻ was based on literature [D. J. Heldebrant, P. G. Jessop, C. A.Thomas, C. A. Eckert, C. L. Liotta, The Reaction of1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide, J. Org.Chem. 70 (2005), 5335-5338. Incorporated herein by reference in itsentirety]. The presence of carbon marked ‘k’ signal at 164.4 ppm wasassigned to the carbamate group [NHC(═O)O⁻]; the absence of any signalat ≈174 ppm precluded the presence of amide group [NHC(═O)C—] whichwould have been generated by hydrolysis of the imidazoline groups. [Y.Duda, R. G. Rueda, M. Galicia, H. I. Beltran, L. S. Z. Rivera, Corrosioninhibitors: Design, performance, and computer simulations. J. Phys.Chem. B, 109 (2005) 22674-22684. Incorporated herein by reference in itsentirety.] The reaction in the presence of CO₂ is presented in Scheme 4.

Imidazoline VIIIa is expected to give rise to the bicarbonate saltVIIIa-H⁺HCO₃ ⁻ as a result of protonation of the amidine motif; thereaction of the primary amine group (NH₂) would furthermore lead to theformation of carbamic acid. [P. N. Sutar, A. Jha, P. D. Vaidya, E. Y.Kenig, Secondary amines for CO₂ capture: A kinetic investigation usingN-ethylmonoethanolamine, Chem. Eng. J. 207-208 (2012) 718-724.Incorporated herein by reference in its entirety.] In a similarexperiment carried out in H₂O, the residue was subsequently vacuum driedafter being treated with flowing CO₂, followed by removal of thesolvent, at room temperature. The IR spectrum of the residue revealedthe absence of any peak around 1640 cm⁻¹ thereby asserting that thehydrolysis of the amidine group to an amide group did not occur; thepresence of a peak at 1610 cm⁻¹ indicated the presence of a protonatedamidine [C═N—H⁺] W. Qiao, Z. Zheng, Q. Shi, Synthesis and properties ofa series of CO2 switchable surfactants with imidazoline group, J.Surfact. Deterg. 15 (2012) 533-539. Incorporated herein by reference inits entirety.] The ¹³C NMR spectrum of the residue revealed the absenceof a HCO₃ ⁻ carbon signal; however, it indicated the presence of threecarbon signals at 162.5, 164.3 and 167.2 ppm which are attributed to thecarbons marked i, k and e, respectively, of VIIIa-CO₂ as shown in FIG.11B. The spectral analyses thus confirmed the formation of bicarbonatesalt VIIIa, followed by bicarbonate/carbamic acid VIIIa-H⁺(HCO₃ ⁻)CO₂,(shown in FIG. 11C) in aqueous solution. However, in the absence ofwater, carbonic acid was lost in the form of CO₂/H₂O to give thezwitterionic carbamate VIIIa-CO₂, as indicated in FIG. 11B.

The study details the chemical reactions of imidazoline in aqueous CO₂,and confirms the effectiveness of corrosion inhibitors bearingelectron-rich amidine groups.

The compounds acted mainly as anodic inhibitors, with ΔG^(o) _(ads)values indicative of chemisorption and XPS results ascertained theformation of an adsorbed protective film in CO₂-saturated 0.5 M NaCl.The adsorption process of the imidazolines was found to obey theLangmuir adsorption isotherm. The surface coverage data and CMC valuesdemonstrated that the inhibitor molecules have a greater tendency toundergo adsorption on to the metal surface than to form micelles. Inautoclave tests under high CO₂ pressure (10 bar) and a temperature of120° C. the imidazolines VIII b, c and IX b, c all performed superior incorrosion inhibition as compared to Q180-E and ARMOHIB 219, twocommercial inhibitors tested for this purpose. These findings, asdisclosed herein, confirm the function of said imidazolinesincorporating electron-rich aromatic group in conjugation to the N═C—Ngroups.

The present disclosure relates to imidazoline compounds, a method offorming said compounds, and their use in preventing, or inhibiting,corrosion.

The examples below are intended to further illustrate protocols forpreparing and characterizing the various embodiments of imidazolinecompounds described herein, and are not intended to limit the scope ofthe claims

Example 1 Materials

Diethylenetetramine (DETA) (99.5%) and tetraethylenepentamine (TEPA)(˜60% purity) were obtained from Aldrich Chemicals. TEPA was purified asdescribed before [M. W. S. Jawich, G. A. Oweimreen, S. A. Ali,Heptadecyl-tailed mono- and bis-imidazolines: A study of the newlysynthesized compounds on the inhibition of mild steel corrosion in acarbon dioxide-saturated saline medium, Corros. Sci. 65 (2012) 104-112.Incorporated herein by reference in its entirety.] p-Hydroxybenzoic acid(I), cysteine hydrochloride, bromoalkane [R—Br (II)] and SOCl₂ fromFluka Ag (Buchs, Switzerland) were used as received. All solvents wereof reagent grade.

Physical Methods

All m.p.s are uncorrected. IR spectra were recorded on a Perkin Elmer16F PC FTIR spectrometer and 1H and ¹³C NMR spectra were measured inCDCl₃ using TMS as internal standard on a JEOL LA 500 MHz NMRspectrometer. Elemental compositions were determined with an ElementalAnalyzer (Carlo-Erba: Model 1106). All the reactions were carried outunder N₂.

Synthesis

General Procedure for the Preparation of Alkyloxybenzoic Acids (III)

Powdered NaOH (40×2.10 mmol) followed by bromoalkane 2 (40×2.16 mmol)were added to a solution of 4-hydroxybenzoic acid (40 mmol) in DMSO (100cm³) under N₂. The reaction mixture in the closed flask was stirredusing magnetic stir bar at 75° C. for 24 h. The reaction mixture wastransferred into water (500 cm³) containing 15 cm³ of concentrated HCl.Crude reaction product revealed the presence of an alkyloxybenzoic acid(III) and its alkyl ester. The organic phase (extracted in ether) waswashed liberally in an excess of water. The ether layer wasconcentrated, and the residual reaction mixture was taken up in ethanol(95% v/v) (100 cm³) and added NaOH (3.00 g, 75 mmol) and heated at 70°C. for 30 min. The mixture was treated with aqueous HCl (500 cm³, 1 M).The solid product (III) was filtered and washed with water, dried andcrystallized from cold pentane.

4-Octyloxybenzoic acid (IIIa)

Yield: 75.6%. Mp 92-95° C. (Found: C, 71.8; H, 8.8. C₁₅H₂₂O₃ requires C,71.97; H, 8.86%); ν_(max) (KBr) 3502 (br), 2926, 2853, 1680, 1604, 1427,1305, 1253, 1166, 1062, 948, 845, and 771 cm⁻¹. δ_(H) (CDCl₃) 0.89 (3H,t, J=7.0 Hz), 1.20-1.55 (10H, m), 1.80 (2H, quint, J=6.8 Hz), 4.02 (2H,t, J=6.7 Hz), 6.94 (2H, d, J=5.2 Hz,), 8.05 (2H, d, J=5.2 Hz). δ_(C)(CDCl₃): 14.08, 22.65, 25.98, 29.08, 29.21, 29.30, 31.79, 68.28, 114.18(2C), 121.38, 132.33 (2C), 163.70, 172.07.

4-Dodecyloxybenzoic acid (IIIb)

Yield: 80.2% (ether). Mp 92-94° C. (Found: C, 74.5; H, 9.9. C₁₉H₃₀O₃requires C, 74.47; H, 9.87%); ν_(max) (KBr) 3448 (br), 2920, 2850, 1682,1604, 1511, 1468, 1427, 1305, 1255, 1167, 946, 845 and 771 cm⁻¹. δ_(H)(CDCl₃) 0.88 (3H, t, J=7.0 Hz), 1.10-1.55 (18H, m), 1.81 (2H, quint,J=6.8 Hz), 4.02 (2H, t, J=6.8 Hz), 6.92 (2H, d, J=8.9 Hz,), 8.05 (2H, d,J=8.9 Hz). δ_(C) (CDCl₃): 14.11, 22.69, 25.96, 29.08, 29.35 (2C), 29.57(2C), 29.64 (2C), 31.91, 68.28, 114.17 (2C), 121.38, 132.33 (2C),163.70, 172.17.

4-Octadecyloxybenzoic acid (IIIc)

Yield: 81.3%. Mp 102-105° C. (Found: C, 76.7; H, 10.7. C₂₅H₄₂O₃ requiresC, 76.87; H, 10.84%); ν_(max) (KBr) 3448 (br), 2919, 2850, 1678, 1604,1469, 1428, 1309, 1256, 1168, 941, 845, and 771 cm⁻¹; δ_(H) (CDCl₃) 0.88(3H, t, J=7.0 Hz), 1.15-1.55 (30H, m), 1.81 (2H, quint, J=6.8 Hz), 4.02(2H, t, J=6.8 Hz), 6.93 (2H, d, J=8.9 Hz,), 8.05 (2H, d, J=8.9 Hz).δ_(C) (CDCl₃): 14.11, 22.69, 25.96, 29.08, 29.36 (2C), 29.70 (10C),31.92, 68.29, 114.19 (2C), 121.38, 132.33 (2C), 164.10, 171.65.

General Procedure for the Synthesis of Alkoxybenzamides (IV)

A mixture of alkoxybenzoic acid (III) (55 mmol) in SOCl₂ (15 cm³) washeated at 80° C. for 30 min. After removal of the excess SOCl₂, theresidual liquid was added drop wise to a 30% NH₃ solution (150 cm³) at0° C. The benzamide (IV) was filtered and dried.

4-Octyloxybenzamide (IVa)

Yield: 93%. Mp 152-153° C. (Found: C, 72.1; H, 9.2; N, 5.5. C₁₅H₂₃NO₂requires C, 72.25; H, 9.30; N, 5.62%); ν_(max) (KBr) 3397, 3172, 2922,2851, 1650, 1610, 1572, 1515, 1468, 1421, 1393, 1305, 1253, 1177, 1145,1120, 1026, 997, 853, 800, 759, 720, 644, and 620 cm⁻¹. δ_(H) (CDCl₃,45° C.) 0.89 (3H, t, J 7.0 Hz), 1.30 (8H, m), 1.45 (2H, m), 1.79 (2H,m), 4.00 (2H, t, J 6.7 Hz), 5.80 (2H, br), 6.91 (2H, d, J 8.9 Hz), 7.76(2H, d, J 8.9 Hz). δ_(C) (CDCl₃, 45° C.): 13.75, 22.36, 25.75, 28.91,28.93, 29.05, 31.53, 68.07, 114.12 (2C), 125.23, 129.00 (2C), 162.05,168.66.

4-Dodecyloxybenzamide (IVb)

Yield: 87%. Mp 143-145° C. (Found: C, 74.5; H, 10.0; N, 4.5. C₁₉H₃₁NO₂requires C, 74.71; H, 10.23; N, 4.59%); ν_(max) (KBr) 3387, 3179, 2921,2851, 1647, 1611, 1572, 1516, 1469, 1421, 1395, 1308, 1256, 1175, 1145,1120, 1019, 844, 799, 723, and 621 cm⁻¹; δ_(H) (CDCl₃, 45° C.) 0.88 (3H,t, J 7.0 Hz), 1.30 (16H, m), 1.45 (2H, m), 1.79 (2H, m), 4.00 (2H, t, J6.7 Hz), 5.80 (2H, br), 6.91 (2H, d, J 8.9 Hz), 7.76 (2H, d, J 8.9 Hz).δ_(C) (CDCl₃, 45° C.): 14.13, 22.69, 25.98, 29.12, 29.37 (2C), 29.56,29.59, 29.64, 29.65, 31.92, 68.23, 114.27 (2C), 125.23, 129.25 (2C),162.23, 168.93.

4-Octadecyloxybenzamide (IVc)

Yield: 95%. Mp 138-139° C. (Found: C, 76.8; H, 10.9; N, 3.5. C₂₅H₄₃NO₂requires C, 77.07; H, 11.12; N, 3.59%); ν_(max) (KBr) 3426, 3195, 2919,2849, 1649, 1616, 1577, 1515, 1471, 1424, 1397, 1307, 1252, 1180, 1145,1120, 1035, 845, 781, and 719 cm⁻¹; δ_(H) (CDCl₃, 45° C.) 0.88 (3H, t, J7.0 Hz), 1.27 (28H, m), 1.45 (2H, m), 1.79 (2H, m), 4.00 (2H, t, J 6.7Hz), 5.70 (2H, br), 6.91 (2H, d, J 8.9 Hz), 7.75 (2H, d, J 8.9 Hz).δ_(C) (CDCl₃, 45° C.): 14.04, 22.66, 26.01, 29.17, 29.35 (3C), 29.68(9C), 31.92, 68.33, 114.39 (2C), 125.23, 129.26 (2C), 162.50, 168.79.

General Procedure for the Synthesis of Alkoxybenzonitriles (V)

A mixture of alkoxybenzamide IV (45 mmol) in SOCl₂ (70 mmol) in benzene(20 cm³) was heated at 80° C. for 1 h or until the reaction was completeas indicated by TLC experiment (silica, Et₂O/MeOH 9:1). After removal ofthe excess SOCl₂, the residual liquid was crystallized from pentane togive the benzonitrile (V).

4-Octyloxybenzonitrile (Va)

Yield: 86%. Mp 32-34° C. (Found: C, 77.6; H, 9.1; N, 5.9. C₁₅H₂₁NOrequires C, 77.88; H, 9.15; N, 6.05%); ν_(max) (KBr) 2927, 2857, 2224,1605, 1573, 1508, 1468, 1391, 1301, 1259, 1171, 1114, 1020, 836, and 706cm⁻¹; δ_(H) (CDCl₃) 0.88 (3H, t, J 7.0 Hz), 1.30 (8H, m), 1.44 (2H, m),1.78 (2H, m), 3.99 (2H, t, J 6.7 Hz), 6.92 (2H, d, J 8.9 Hz), 7.56 (2H,d, J 8.9 Hz). δ_(C) (CDCl₃): 14.01, 22.55, 25.85, 28.90, 29.11, 29.19,31.70, 68.34, 103.53, 115.10 (2C), 119.24, 133.85 (2C), 162.39.

4-Dodecyloxybenzonitrile (Vb)

Yield: 87%. Mp 49-50° C. (Found: C, 79.1; H, 9.9; N, 4.8. C₁₉H₂₉NOrequires C, 79.39; H, 10.17; N, 4.87%); ν_(max) (KBr) 2916, 2848, 2217,1607, 1573, 1508, 1472, 1397, 1302, 1257, 1170, 1115, 1029, 1002, 832,813, and 716 cm⁻¹; δ_(H) (CDCl₃) 0.88 (3H, t, J 7.0 Hz), 1.31 (16H, m),1.44 (2H, m), 1.80 (2H, m), 3.99 (2H, t, J 6.7 Hz), 6.92 (2H, d, J 8.9Hz), 7.56 (2H, d, J 8.9 Hz). δ_(C) (CDCl₃): 14.13, 22.69, 25.93, 28.97,29.32, 29.35, 29.54, 29.57, 29.65 (2C), 31.92, 68.42, 103.61, 115.17(2C), 119.36, 133.95 (2C), 162.46.

4-Octadecyloxybenzonitrile (Vc)

Yield: 93%. Mp 69-70° C. (Found: C, 80.6; H, 10.9; N, 3.7. C₂₅H₄₁NOrequires C, 80.80; H, 11.12; N, 3.77%); ν_(max) (KBr) 2917, 2848, 2217,1607, 1573, 1508, 1472, 1398, 1302, 1258, 1170, 1115, 1035, 833, 812,and 718 cm⁻¹; δ_(H) (CDCl₃) 0.88 (3H, t, J 7.0 Hz), 1.28 (28H, m), 1.44(2H, m), 1.80 (2H, m), 3.99 (2H, t, J 6.7 Hz), 6.92 (2H, d, J 8.9 Hz),7.56 (2H, d, J 8.9 Hz). δ_(C) (CDCl₃): 14.07, 22.64, 25.87, 28.92,29.27, 29.32, 29.48, 29.52, 29.65 (8C), 31.87, 68.35, 103.54, 115.09(2C), 119.25, 133.86 (2C), 162.39.

General procedure for the synthesis of1-(2-aminoethyl)-2-alkoxyphenyl)-2-imidazolines (VIII)

A solution of alkoxybenzonitrile (V) (25 mmol) and diethylenetriamine(VI) (DETA) (62 mmol) containing cysteine-HCl (100 mg) was heated at145° C. for 1 h. Thereafter, another portion of cysteine-HCl (100 mg)was added and the reaction mixture was heated at 145° C. for anadditional 1 h. Evolution of NH₃ gas was observed which bubbled throughthe connected U-tube containing mineral oil. ¹H NMR indicated thecompletion of the reaction. The reaction mixture was cooled and taken upin CH₂Cl₂ (50 cm³). The unreacted DETA was removed from the organiclayer by washing with water (3×300 cm³); very careful agitation wasrequired to avoid emulsion formation. Concentration of the dried(Na₂SO₄) organic layer afforded the imidazolines (VIII) as a pinkishliquid/semisolid. The imidazolines were pure as indicated by NMR spectraand used as such for the corrosion inhibition efficiency tests. Thenewly synthesized imidazolines gave satisfactory elemental analysesgiven the fact these compounds cannot be further purified bycrystallization.

1-(2-Aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline (VIIIa)

Yield: 70%. ν_(max) (neat) 3278, 2926, 2856, 1609, 1512, 1468, 1391,1328, 1296, 1249, 1175, 1085, 1026, 950, and 839 cm⁻¹; δ_(H) (CDCl₃):0.88 (3H, t, J 6.7 Hz), 1.20-1.50 (12H, m), 1.77 (2H, m), 2.86 (2H, t, J6.4 Hz), 3.12 (2H, t, J 6.4 Hz), 3.43 (2H, t, J 9.5 Hz), 3.90 (2H, t, J9.5 Hz), 3.97 (2H, t, J 6.4 Hz), 6.90 (2H, d, J 8.9 Hz), 7.50 (2H, J 8.9Hz). δ_(C) (CDCl₃): 13.73, 22.28, 25.65, 28.84 (2C), 28.97, 31.43,40.68, 51.10, 52.50, 52.88, 67.69, 113.92 (2C), 123.04, 129.33 (2C),159.96, 167.52.

1-(2-Aminoethyl)-2-(4-dodecyloxyphenyl)-2-imidazoline (VIIIb)

Yield: 83%. ν_(max) (neat) 3248, 2922, 2852, 1646, 1612, 1513, 1467,1418, 1392, 1329, 1297, 1249, 1174, 1085, 1051, 1012, 950, 839, and 723cm⁻¹; δ_(H) (CDCl₃): 0.88 (3H, t, J 6.7 Hz), 1.20-1.50 (20H, m), 1.77(2H, m), 2.85 (2H, t, J 6.4 Hz), 3.11 (2H, t, J 6.4 Hz), 3.43 (2H, t, J9.7 Hz), 3.88 (2H, t, J 9.8 Hz), 3.96 (2H, t, J 6.4 Hz), 6.88 (2H, d, J8.7 Hz), 7.49 (2H, J 8.7 Hz); δ_(C) (CDCl₃): 13.96, 22.51, 25.85, 29.00,29.18, 29.22, 29.42, 29.46 (2C), 29.48, 31.73, 40.87, 51.28, 52.69,53.08, 67.85, 114.08 (2C), 123.21, 129.41 (2C), 160.13, 167.71.

1-(2-Aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline (VIIIc)

Yield: 95%. ν_(max) (KBr) 3387, 2917, 2849, 1612, 1513, 1468, 1418,1394, 1329, 1297, 1250, 1175, 1036, 837, and 721 cm⁻¹; δ_(H) (CDCl₃):0.88 (3H, t, J 6.7 Hz), 1.20-1.50 (32H, m), 1.78 (2H, m), 2.85 (2H, t, J6.1 Hz), 3.12 (2H, t, J 6.1 Hz), 3.44 (2H, t, J 9.8 Hz), 3.88 (2H, t, J9.8 Hz), 3.96 (2H, t, J 6.4 Hz), 6.88 (2H, d, J 8.7 Hz), 7.49 (2H, J 8.7Hz). δ_(C) (CDCl₃): 13.97, 22.53, 25.87, 29.04, 29.16, 29.21, 29.24,29.37, 29.42, 29.45, 29.51 (2C), 29.55 (4C), 31.77, 40.86, 51.27, 52.65,52.97, 67.88, 114.11 (2C), 123.14, 129.55 (2C), 160.19, 167.71.

General procedure for the synthesis of1-[2-{2-(2-Aminoethylamino)-ethylamino}ethyl]-2-alkoxyphenyl-2-imidazolines(IX)

A solution of mono-alkoxybenzonitriles (V) (25 mmol) andtetraethylenepentamine (VII) (TEPA) (62 mmol) containing cysteine-HCl(100 mg) was heated a 145° C. for 1 h. Thereafter, another portion ofcysteine-HCl (100 mg) was added and the reaction mixture was heated at145° C. for an additional 1 h. Evolution of NH₃ gas was observed whichbubbled through the connected U-tube containing mineral oil. ¹H NMRindicated the completion of the reaction. The reaction mixture wascooled and taken up in CH₂Cl₂ (50 cm³). An equivalent workup asdescribed under the prior general procedure for the synthesis of1-(2-aminoethyl)-2-alkoxyphenyl)-2-imidazolines afforded theimidazolines (IX) as a pinkish liquid/semisolid. The imidazolines werepure enough as indicated by NMR spectra and used as such for thecorrosion tests.

1-[2-{2-(2-Aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazoline(IXa)

Yield: 78%. ν_(max) (neat) 3286, 2924, 2853, 1612, 1514, 1467, 1420,1393, 1331, 1296, 1249, 1174, 1114, 1026, 950, 838, and 740 cm⁻¹; δ_(H)(CDCl₃): 0.89 (3H, t, J 6.7 Hz), 1.20-1.65 (14H, m), 1.77 (2H, m), 2.67(2H, t, J 5.8 Hz), 2.73 (4H, s), 2.77 (2H, t, J 6.7 Hz), 2.80 (2H, t, J6.0 Hz), 3.19 (2H, t, J 6.4 Hz), 3.42 (2H, t, J 9.7 Hz), 3.88 (2H, t, J9.7 Hz), 3.96 (2H, t, J 6.4 Hz), 6.89 (2H, d, J 8.9 Hz), 7.50 (2H, J 8.9Hz). δ_(C) (CDCl₃): 14.11, 22.64, 26.00, 29.17, 29.21, 29.33, 31.78,41.81, 48.54, 49.25, 49.57, 49.99, 51.55, 52.51, 53.19, 68.03, 114.24(2C), 123.37, 129.67 (2C), 160.29, 167.77.

1-[2-{2-(2-Aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazoline(IXb)

Yield: 77%. ν_(max) (neat) 3282, 2924, 2853, 1613, 1514, 1466, 1420,1390, 1330, 1296, 1249, 1173, 1115, 1069, 1011, 949, 838, and 735 cm⁻¹;δ_(H) (CDCl₃): 0.88 (3H, t, J 6.7 Hz), 1.20-1.70 (22H, m), 1.78 (2H, m),2.67 (2H, t, J 5.8 Hz), 2.73 (4H, s), 2.78 (2H, t, J 6.6 Hz), 2.81 (2H,t, J 6.1 Hz), 3.19 (2H, t, J 6.4 Hz), 3.44 (2H, t, J 9.7 Hz), 3.88 (2H,t, J 9.7 Hz), 3.96 (2H, t, J 6.4 Hz), 6.89 (2H, d, J 8.9 Hz), 7.50 (2H,J 8.9 Hz). δ_(C) (CDCl₃): 14.13, 22.68, 26.02, 29.18, 29.35, 29.38,29.60 (2C), 29.63 (2C), 31.92, 41.83, 48.56, 49.26, 49.58, 50.00, 51.57,52.55, 53.24, 68.04, 114.25 (2C), 123.30, 129.67 (2C), 160.14, 167.78.

1-[2-{2-(2-Aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazoline(IXc)

Yield: 93%. ν_(max) (neat) 3480, 2914, 2847, 1599, 1513, 1466, 1420,1387, 1331, 1248, 1174, 1115, 837, and 722 cm⁻¹. δ_(H) (CDCl₃): 0.88(3H, t, J 6.7 Hz), 1.20-1.60 (34H, m), 1.78 (2H, m), 2.68 (2H, t, J 5.5Hz), 2.73 (4H, s), 2.78 (2H, t, J 6.5 Hz), 2.81 (2H, t, J 5.8 Hz), 3.19(2H, t, J 6.4 Hz), 3.43 (2H, t, J 9.7 Hz), 3.88 (2H, t, J 9.7 Hz), 3.96(2H, t, J 6.4 Hz), 6.89 (2H, d, J 8.9 Hz), 7.50 (2H, J 8.9 Hz). δ_(C)(CDCl₃): 14.14, 22.69, 26.03, 29.20, 29.37, 29.41, 29.60, 29.63, 29.70(8C), 31.93, 41.86, 48.59, 49.29, 49.62, 50.04, 51.60, 52.58, 53.28,68.04, 114.25 (2C), 123.42, 129.68 (2C), 160.30, 167.80.

Specimens

For the electrochemical tests, corrosion studies were carried out withmild steel coupons of the following composition: 0.089% (C), 0.037 (Cr),0.34% (Mn), 0.022 (Ni), 0.010 (P), 0.007 (Mo), 0.005 (V), 0.005 (Cu),99.47% (Fe). A 1 mm thick mild steel sheet was machined to a flag shapewith a stem approximately 3 cm in length. Insulating the stem byaraldite (affixing material) provided 2 cm² exposed area which wasabraded with increasing grades of emery papers (100, 400, 600 and 1500grit size), washed with distilled deionized water and acetone prior todrying in an oven at 110° C. The dried specimens were stored in adesiccator until being used. Immediately before use, the electrodespecimens were placed in an ultrasonic bath for 5 minutes and thenwashed with distilled water.

For autoclave tests, the two types of mild steel coupons A and Bmeasuring ≈2.5×2.0×0.1 cm³ have the following composition:

Coupon A: 0.082% (C), 0.016% (Cr), 0.207% (Mn), 0.062% (Ni), 0.029%(Cu), 0.012% (Mo), <0.001% (V), 0.032% (Si), <0.0005% (P), 0.0059% (S),0.011% (Co), 0.045% (Al), <0.0010 (Nb), <0.0005% (Ti), <99.3% (Fe).

Coupon B: 0.168% (C), 0.038% (Cr), 0.495% (Mn), 0.034% (Ni), 0.074%(Cu), 0.0081% (Mo), 0.001% (V), 0.237% (Si), 0.014% (P), 0.024% (S),0.011% (Co), 0.080% (Al), 0.0019 (Nb), 0.0015% (Ti), <98.6% (Fe).

Solutions

Corrosion inhibition tests have been performed in 0.5 M NaCl in thepresence of CO₂ (1 atm) at 40° C. as well as at higher pressure (10 bar)of CO₂ and temperature of 120° C. De-aeration of the solution wasachieved by purging with 99.999% N₂ (30 min) and then the solution wassaturated by continuously bubbling with 99.999% pure CO₂. Duringpolarization measurements, instead of bubbling, the gentle flow of CO₂was maintained above the surface of the solution without agitating thebulk of the solution. The corrosion caused by oxygen is avoided by theuse of the high purity CO₂. In an aqueous solution of CO₂, at pH<4 thecorrosion usually occurs by reaction with H⁺, while above pH 4 theactive species is adsorbed CO₂ or H₂CO₃ [S. Nesic, K. L. J. Lee, Amechanistic model for carbon dioxide corrosion of mild steel in thepresence of protective iron carbonate films-part 3: film growth model,Corrosion, 59 (2003) 616-627. Incorporated herein in its entirety]. Inorder to avoid any change in the corrosion mechanism, a solution ofNaHCO₃ (100 mg/L) was used to maintain the pH between 5.0 and 5.5.

Electrochemical Measurements

Tafel Extrapolations

The polarization studies were carried out in a 250 cm³ of 0.5 M NaClsolution at 40° C. in the presence of CO₂ (1 atm), and furthermore, inboth the absence and presence of inhibitors at various concentrationthereof. The electrochemical cell, assembled in a 750 cm³ round-bottomflask, consisted of a saturated calomel electrode (SCE) as a referenceelectrode, a mild steel working electrode, and a graphite electrode (≈5mm diameter) as a counter electrode. The bubbler has one outlet andinlet for the CO₂. The polarization curves were recorded by a computercontrolled potentiostat-galvanostat (Auto Lab, Booster 10A-BST707A, EcoChemie, Netherlands). A computer (Windows 7) loaded with NOVA (Version1.8) software processed the data. All three electrode cells wereconnected to the potentiostat (Auto Lab), and used for measurements. Astable open circuit potential was achieved after pre-corroding theworking electrode in the solution; within a time frame of 30-60 min. Ascan of ±250 mV with respect to the open circuit potential E_(corr) isconducted at a rate of 0.5 mV/s.

Linear Polarization Resistance (LPR) Method

The cell described above was also used for the LPR measurement. Thecurrent potential plots (in a range of ±10 mV around E_(corr)) providedthe polarization resistance values.

Gravimetric Measurements at High Temperature and Pressure: AutoclaveExperiments

The weight-loss measurements at a high temperature of 120° C. and a CO₂pressure of 10 bar in 0.5 M NaCl solution (250 cm³) in the absence andpresence of inhibitors (200 ppm) was carried out in a R&D AutoclaveBolted Closure System (Autoclave Engineers, Model #401C-0679) for 48 h.The detailed experimental procedure is described in our earlier work [M.A. J. Mazumder, H. A. Al-Muallem, M. Faiz, S. A. Ali, Design andsynthesis of a novel class of inhibitors for mild steel corrosion inacidic and carbon dioxide-saturated saline media, Corros. Sci. (2014),DOI: 10.1016/j. Incorporated herein by reference in its entirety]. Thecarbon-steel coupons prepared as described (vide supra) were immersedinto the test solution.

Measurement of Surface Tension

The surface tension of the imidazoline samples in 0.5 M NaCl solution at40° C. were measured by PHYWE surface tensiometer (Germany) followingthe operating principle of the du Nouy ring method. The surfacetensiometer equipped with a torsion dynamometer (0.01 N) and a platinumiridium ring with a diameter of 1.88 cm was used to measure the tear offforce. Solutions of different concentrations were prepared from 0.5 MNaCl and equilibrated to 40° C. Solutions of CO₂ saturated 0.5 M NaClwas made by passing CO₂ gas at 40° C.

The Standard Free Energy of Micelle Formation (ΔG^(o) _(mic))

The ΔG^(o) _(mic) of the synthesized imidazoline surfactant is given byEq. (6):

ΔG ^(o) _(mic) =RT ln(C _(cmc)/mol L⁻¹)  (6)

[H.-J. Butt, K. Graf, M. Kappl, Physics and Chemistry of Interfaces.Wiley-VCH, Weinheim, 2003 pp. 253 Incorporated herein in its entirety.]where R, T and C_(cmc), represent the gas constant, temperature andconcentration of the surfactant at the critical micelle concentration(CMC).

X-Ray Photoelectron Spectroscopy

The metal coupons of dimension of 2.5×2.0×0.1 cm³ as treated in theelectrochemical tests in CO₂ saturated 0.5 M NaCl at 40° C. for 6 h wererinsed with distilled deionized water and dried under N₂. The XPSanalysis, using Advantage software for all data processing, wasperformed using a Thermos Scientific X-ray photoelectron spectrometer(Model # Escalab 250 Xi) and the samples were irradiated withmonochromated Al K_(α) X-rays (1486.6 eV) of spot size of diameter 650The spectra were referenced with a C is peak at 285.4 eV. XPS spectrawere deconvoluted using a non-linear least squares algorithm with aShirley base line and a Gaussian-Lorentzian combination.

Synthesis of the Corrosion Inhibitors

As outlined in Scheme 2, p-hydroxybenzoic acid was O-alkylated to givep-alkoxycarboxylic acid in excellent yields. A mixture of an equimolaramount of the acid and DETA was heated at temperatures ranging from185-250° C. initially using a procedure as described in: Y. Wu, P. R.Herrington, Thermal reactions of fatty acids with diethylene triamine.J. Am. Oil Chem. Soc. 74 (1997) 61-64, and Y. Duda, R. G. Rueda, M.Galicia, H. I. Beltran, L. S. Z. Rivera, Corrosion inhibitors: Design,performance, and computer simulations. J. Phys. Chem. B, 109 (2005)22674-22684, which are incorporated herein by reference in theirentirety, in order to generate the imidazolines (VIII). However, acomplicated mixture of products that contained variable amounts of theunreacted acid and amide along with the desired imidazoline (VIII)(≈50%) was obtained. This mixture may as well serve as an effectiveinhibitor mixture. However, one objective was to synthesize anddetermine the inhibition efficiencies of the pure imidazolines alone. Inorder to pursue the synthesis of the proposed imidazolines, a differentsynthetic protocol was designed; the use of nitrile (CN) instead of anacid (CO₂H) group was envisaged. For this purpose, nitriles have beenprepared in excellent yields as illustrated in Scheme 2. The reaction ofthe nitrile with DETA was carried out using the procedure as mentionedin U.S. Pat. No. 4,420,619, [A. Marxer, Imidazole urea and amidocompounds. (1983), Incorporated herein by reference in its entirety.]However, the use of CS₂ as a catalyst failed to give the imidazoline(VIII) in the temperature range 110-145° C. A further modification ofthe catalyst to cysteine HCl, and maintaining a precise temperaturerange of 140° C. to 150° C., led to the formation of the imidazolines(VIII) and (IX) using DETA (VI) and TEPA (VII), respectively, withexcellent yields. In a most preferred embodiment, the reactiontemperature is maintained at 145° C. The imidazolines were readilyidentified by ¹H and ¹³C NMR spectroscopy. The ¹H NMR spectra of theimidazolines Villa and IXa and a ¹³C NMR spectra of VIIIc and IXc areshown in FIGS. 3 and 4, respectively. The carbon spectra revealed thepresence of four and eight signals for the carbons marked as a-d and a-hin VIIIc and IXc, respectively.

Preparing a series of imidazolines, bearing different N-substituents andalkoxy chains, allows for the assessment and comparison of theirinhibition effects. Two commercial inhibitor samples: QI80-E (R═C₁₂ toC₂₂) from Materials Performance and ARMOHIB 219 from AKZO NOBEL werealso tested for the purpose of comparison and are shown below:

Electrochemical Measurements

Tafel Extrapolation

The corrosion inhibition results of inhibitors VIIIa-c and IXa-c,carried out in a CO₂-saturated 0.5 M NaCl solution using Tafel plotextrapolation, are summarized in Tables 1 and 2. The pH was kept in therange of 5.0-5.5 to minimize the direct reduction of H₂CO₃ (Eq. 1) [W.Durnie, R. De Marco, A. Jefferson, B. Kinsella, Development of astructure-activity relationship for oil field corrosion inhibitors, J.Electrochem. Soc. 146 (1999) 1751-1756. S. Nesic, G. T. Solvi, J.Enerhaug, Comparison of the rotating cylinder and pipe flow tests forflow-sensitive carbon dioxide corrosion, Corrosion 10 (1995) 51773-787.Incorporated herein by reference in their entirety]. Some representativeTafel plots are shown in FIGS. 5A, 5B, 5C, and 5D. Each pair of Tafelplots was analyzed [S. A. Ali, M. T. Saeed, S. U. Rahman, Theisoxazolidines: a new class of corrosion inhibitors of mild steel inacidic medium, Corros. Sci. 45 (2003) 253-266. Incorporated herein byreference in its entirety.] in order to obtain the corrosion currentdensity (i_(corr)) and the corrosion potential (E_(corr)). Theextrapolation of cathodic Tafel lines with respect to free corrosionpotential from Tafel plots was determined by using a computer (Windows7) controlled potentiostat-galvanostat (AutoLab, Eco Chemie,Netherlands) instrument with the utilization of an automated linearcurve fitting Nova 1.8 software.

LPR

The η % from a LPR technique was calculated using Eq. (7):

$\begin{matrix}{{\eta (\%)} = {( \frac{R_{p}^{\prime} - R_{p}}{R_{p}^{\prime}} )x\; 100}} & (7)\end{matrix}$

where R_(p) and R′_(P) are the respective polarization resistances insolution without or with the inhibitors in CO₂-saturated 0.5 M NaCl at40° C. (Tables 3 and 4). Tables 3 and 4 also include inhibition dataobtained at 30° C. and 50° C. The results of the Tafel extrapolation andLPR at 40° C. are compared in Table 5.

Adsorption Isotherms

Fractional inhibition efficiency η, equated to surface coverage θ of theelectrode by an inhibitor molecule at its lower concentration range, isreported in Tables 1-4. Note that at higher inhibitor concentrations,the η versus θ relationship does not remain linear owing to a transitionfrom a monolayer to a multilayer coverage. The θ values obtained by theLPR method (Tables 3 and 4) in CO₂-saturated 0.5 M NaCl, and C (theconcentration in mol/L), were used to find the best among the followingadsorption isotherms, namely:

Temkin: K _(ads) C=e ^(fθ)  (8)

Langmuir: θ/(1−θ)=K _(ads) C  (9)

Frumkin [37]: K _(ads) C={θ/(1−θ)}e ^(−2aθ)  (10)

Freundluich [38]: θ=K _(ads) C ^(n)  (11)

where K_(ads) is the equilibrium constant of the adsorption process. Thecorrelation coefficient revealed the best fit for the Langmuir isothermfor the inhibitors in CO₂ saturated 0.5 M NaCl in FIGS. 6A, 6B, 6C, and6D, and it is also presented in Table 6. Some of the inhibitorsdemonstrated a good fit for both the Temkin, as well as Langmuir,adsorption isotherms. The molecular interaction parameter f, whichdescribes molecular interactions in the adsorption layer as well asinhomogeneities on the surface of the electrode, was calculated from theTemkin isotherm (Table 6). [W. Durnie, R. De Marco, A. Jefferson, B.Kinsella, Development of a structure-activity relationship for oil fieldcorrosion inhibitors, J. Electrochem. Soc. 146 (1999) 1751-1756. J. O'M.Bockris, S. U. M. Khan, Surface electrochemistry: A molecular levelapproach, Plenum press, New York and London, 1993. Incorporated hereinby reference in their entirety.]

The K_(ads) is related to the free energy of adsorption (ΔG^(o) _(ads)),by:

$\begin{matrix}{K_{ads} = {\frac{1}{55.5}{\exp ( \frac{{- \Delta}\; G_{ads}^{o}}{RT} )}}} & (12)\end{matrix}$

The values of K_(ads) and ΔG^(o) _(ads) are summarized in Table 7. TheΔS^(o) _(ads) and ΔH^(o) _(ads) for the adsorption process of theimidazolines VIIIc and IXc in the temperature range of 30-50° C. wasobtained from a plot of ΔG^(o) _(ads) versus T as shown in FIG. 7.

Gravimetric Measurements in CO₂-Saturated 0.5 M NaCl at High Temperatureand Pressure

The results of the experiments carried out at temperature of 120° C. anda pressure of 10 bar CO₂ in 0.5 M NaCl for 48 h are given in Table 8.Duplicate determinations were made in each case using coupons of almostidentical masses. Percent inhibition efficiency (i %) was calculatedusing Eq. (13):

$\begin{matrix}{{\eta \mspace{14mu} \%} = {\frac{{{Weight}\mspace{14mu} {{loss}({blank})}} - {{Weight}\mspace{14mu} {{loss}({inhibitor})}}}{{Weight}\mspace{14mu} {{loss}({blank})}} \times 100}} & (13)\end{matrix}$

Where the masses of the coupons differed, relative weight loss of thecoupons were used to calculate the η % [S. A. Ali, M. T. Saeed, S. U.Rahman, The isoxazolidines: a new class of corrosion inhibitors of mildsteel in acidic medium, Corros. Sci. 45 (2003) 253-266.6, S. A. Ali, H.A. Al-Muallem, M. T. Saeed, S. U. Rahman, Hydrophobic-tailedbicycloisoxazolidines: A comparative study of the newly synthesizedcompounds on the inhibition of mild steel corrosion in hydrochloric andsulfuric acid media, Corros. Sci. 50 (2008) 664-675. Incorporated hereinby reference in their entirety]. The average η %, as reported in Table8, is found to have a standard deviation of 2-3%.

Surface Tension

The surface tension γ and critical CMC values for the imidazolines VIIIand IX are measured in 0.5 M NaCl and 0.5 M NaCl+CO₂ at 40° C. and theresults are given in Table 9. FIGS. 8A, 8B show the plot of surfacetension γ against the concentration of the imidazolines under variousconditions.

X-Ray Photoelectron Spectroscopy

The plots of the intensity (counts) versus binding energy (eV) asmeasured by XPS are shown in FIGS. 9A, 9B, 9C, 9D, 9E, 9F and 10A, 10B,10C. The results of the surface analysis are given in Table 10.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, defines, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

1: A corrosion inhibiting composition comprising an aminoalkylimidazoline of formula (I)

wherein m is an integer of 1 to 10; R is a C₁-C₆ alkylene; R₁ isselected from the group consisting of aromatic hydrocarbons of formula(II)

further wherein X is a heteroatom independently selected from the groupconsisting of oxygen, and sulfur; R′₁ thru R′₅ are each independentlyselected from the group consisting of hydrogen, C₁-C₃₀ alkyl, alkenyl,aryl, alkylaryl, arylalkyl, aminoalkyl, and aminoaryl; R₂ and R₃ and areeach independently selected from the group consisting of hydrogen,hydroxyl, halogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl, arylalkyl,aminoalkyl, aminoaryl, (CH₂)₂COOH, CH₂CH(CH₃)COOH, and imidazoline. 2:The composition of claim 1 wherein the aminoalkyl imidazoline comprisesa 2-imidazoline ring substituted with: an ethanamine group at a 5-Nposition of the 2-imidazoline ring, and a p-octyloxy phenyl group at a1-C position of the 2-imidazoline ring. 3: The composition of claim 1wherein the aminoalkyl imidazoline comprises a 2-imidazoline ringsubstituted with: an ethanamine group at a 5-N position of the2-imidazoline ring, and a p-dodecyloxy phenyl group at a 1-C position ofthe 2-imidazoline ring. 4: The composition of claim 1 wherein theaminoalkyl imidazoline comprises a 2-imidazoline ring substituted with:an ethanamine group at a 5-N position of the 2-imidazoline ring, and ap-octadecyloxy phenyl group at the 1-C position of the 2-imidazolinering. 5: The composition of claim 1 wherein the aminoalkyl imidazolinecomprises a 2-imidazoline ring substituted with: aN¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine group at a 5-N position ofthe 2-imidazoline ring, and a p-octyloxy phenyl group at a 1-C positionof the 2-imidazoline ring. 6: The composition of claim 1 wherein theaminoalkyl imidazoline comprises a 2-imidazoline ring substituted with:a N¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine group at a 5-N positionof the 2-imidazoline ring, and a p-dodecyloxy phenyl group at a 1-Cposition of the 2-imidazoline ring. 7: The composition of claim 1wherein the aminoalkyl imidazoline comprises a 2-imidazoline ringsubstituted with: a N¹-(2-aminoethyl)-N²-ethylethane-1,2-diamine groupat a 5-N position of the 2-imidazoline ring, and a p-octadecyloxy phenylgroup at the 1-C position. 8: The composition of claim 1 wherein theaminoalkyl imidazoline is prepared by reacting diethylene triamine(DETA) with 4-(octyloxy) cyclohexanecarbonitrile in the presence of acysteine HCl catalyst at a temperature of 145° C. to yield1-(2-aminoethyl)-2-(4-octyloxyphenyl)-2-imidazoline. 9: The compositionof claim 1 wherein the aminoalkyl imidazoline is prepared by reactingdiethylene triamine (DETA) with 4-(dodecyloxy) cyclohexanecarbonitrilein the presence of a cysteine HCl catalyst at a temperature of 145° C.to yield 1-(2-aminoethyl)-2-(4-dodecyloxyphenyl)-2-imidazoline. 10: Thecomposition of claim 1 wherein the aminoalkyl imidazoline is prepared byreacting diethylene triamine (DETA) with 4-(octadecyloxy)cyclohexanecarbonitrile in the presence of a cysteine HCl catalyst at atemperature of 145° C. to yield1-(2-aminoethyl)-2-(4-octadecyloxyphenyl)-2-imidazoline. 11: Thecomposition of claim 1 wherein the aminoalkyl imidazoline is prepared byreacting tetraethylene pentamine (TEPA) with 4-(octyloxy)cyclohexanecarbonitrile to yield1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octyloxyphenyl)-2-imidazolinein the presence of a cysteine HCl catalyst at a temperature of 145° C.12: The composition of claim 1 wherein the aminoalkyl imidazoline isprepared by reacting tetraethylene pentamine (TEPA) 4-(dodecyloxy)cyclohexanecarbonitrile to yield1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-dodecyloxyphenyl)-2-imidazolinein the presence of a cysteine HCl catalyst at a temperature of 145° C.13: The composition of claim 1 wherein the aminoalkyl imidazoline isprepared by reacting tetraethylene pentamine (TEPA) 4-(octadecyloxy)cyclohexanecarbonitrile to yield1-[2-{2-(2-aminoethylamino)ethylamino}ethyl]-2-(4-octadecyloxyphenyl)-2-imidazolinein the presence of a cysteine HCl catalyst at a temperature of 145° C.14: The composition of claim 1 further comprising one or more additivesselected from the group consisting of surfactants, intensifiers,solvents, oil-wetting components, dispersants, scale inhibitors andbiocides. 15: A method of preventing or reducing corrosion in a processcomprising adding to a process stream an effective corrosion inhibitingamount of one or more aminoalkyl imidazolines of formula (I)

wherein m is an integer of 1 to 10; R is a C₁-C₆ alkylene; R₁ isselected from the group consisting of aromatic hydrocarbons of formula(II)

wherein X is a heteroatom selected from the group consisting of oxygenand sulfur; R′₁ thru R′₅ are each independently selected from the groupconsisting of hydrogen C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl,arylalkyl, aminoalkyl, and aminoaryl; R₂ and R₃ and are eachindependently selected from the group consisting of hydrogen, hydroxyl,halogen, C₁-C₃₀ alkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl,aminoaryl, (CH₂)₂COOH, CH₂CH(CH₃)COOH, and imidazoline. 16: The methodof claim 15 wherein the process stream comprises at least oneconstituent selected from the group comprising water, petroleum,petroleum products, and at least one constituent selected from the groupconsisting of carbon dioxide (CO₂), hydrogen sulfide (H₂S), oxygen (O),and NaCl. 17: The method of claim 15 wherein said effective corrosioninhibiting amount comprises 0.1 to 1,000 ppm by weight of an aminoalkylimidazoline. 18: The method of claim 15 wherein said effective corrosioninhibiting amount comprises 1.0 to 500 ppm by weight of an aminoalkylimidazoline. 19: The method of claim 11 wherein said adding of theaminoalkyl imidazolines is continuous or intermittent. 20: A method ofinhibiting a metal corrosive process of a mild steel surface in contactwith a process stream wherein said process stream comprises at least oneconstituent selected from the group comprising water, petroleum,petroleum products, or mixtures thereof, comprising; administering aneffective concentration of an aminoalkyl imidazoline of claim 1 whereinsaid administering comprises a spraying or a dipping of a mild steelsurface and/or an adding to said process stream contacting said mildsteel surface, of said imidazoline so as to cover and maintain aneffective application on said surface; wherein said effectiveconcentration comprises an amount of 0.1 ppm to 500 ppm; further whereina flow rate of said process stream contacting said mild steel surface isfrom 0-50 m/sec.